Experimental 
Electrical  Testing 


BY  STUDENTS 


Compiled  chiefly  from  data  furnished  by 

SCIENCE  TEACHERS  AND  STUDENTS  IN 
UNIVERSITIES,  COLLEGE  PREPARATORY 
SCHOOLS,  AND  HIGH  SCHOOLS 


For  the  Science  Teacher 


WESTON  ELECTRICAL  INSTRUMENT  CO. 

NEWARK    N.  J. 


EXPERIMENTAL 
ELECTRICAL    TESTING 

A  COMPILATION,  INCLUDING   PRACTICAL   ELECTRICAL 
MEASUREMENTS  ACTUALLY  PERFORMED  BY  STUDENTS 


MONOGRAPH    B-4 

APRIL,   1914. 


ISSUED    FOR 

SCIENCE  TEACHERS  IN  EDUCATIONAL    INSTITUTIONS 


"  Everybody  needs  to  know  something  about  the  working  of  electrical 
machinery,  optical  instruments,  ships,  automobiles,  and  all  those  labor- 
saving  devices,  such  as  vacuum  cleaners,  fireless  cookers,  pressure  cookers 
and  electric  irons,  which  are  found  in  many  American  homes.  We  have, 
therefore,  drawn  as  much  of  our  illustrative  material  as  possible  from  the 
common  devices  in  modern  life.  We  see  no  reason  why  this  should  detract 
in  the  least  from  the  educational  value  of  the  study  of  physics,  for  one  can 
learn  to  think  straight  just  as  well  by  thinking  about  an  electrical  generator, 
as  by  thinking  about  a  Geissler  tube." 

From  ",P.ra£tical  Physios.";  BLACK  &  DAVIS. 


WESTON  ELECTKICAL   INSTRUMENT   CO. 

NEWARK,    N.  J. 


COPYRIGHT.    1914 

BY 
WESTON  ELECTRICAL  INSTRUMENT  CO. 


CONTENTS 


SUBJECTS. 

PAGE 

Argument  ......................................................  5 

(jeneral  Laboratory  Work  ........................................  7 

Resistance  Measurements  ..........................  ..............  11 

A  Complex  Lamp  Bank  ..........................................  13 

Testing  Fuses  ...................................................  17 

Induction  ......................................................  22 

The  Photometer  .................................................  28 

Incandescent  Lamp  Testing  ......................................  32 

Electroplating  ..................................................  34 

The  Use  of  the  Electric  Heater  in  Efficiency  Tests  ..................  38 

The  Electrolytic  Current  Rectifier  .................................  53 

The  Weston  Direct-current  Movable  Coil  System  ....................  65 

The  Weston  Alternating-  and  Direct-current  "  Soft  Iron  "  System  .....  68 

Co-operators  ...................................................  70 

An  Appeal  .....................................................  78 

EXPERIMENTS. 
/ 

1.  Resistance  of  a  Conductor  by  the  Substitution  Method  ..........  11 

2.  Comparative  Resistance  of  Various  Conductors  ..................  13 

3.  Constructing  and  Testing  a  Lamp  Bank  Rheostat  ...............  13 

4.  Test  of  Fuses  ...............................................  17 

5.  The  Fusing  Effect  of  an  Electric  Current  ........................  19 

6.  Currents  Induced  by  Magnetism  .............................  24 

7.  Currents  Induced  by  Electro-Magnetism  .......................  26 

8.  An  Exercise  in  Photometry  ...................................  28 

9.  Practical  Incandescent  Lamp  Testing  ...........................  32 

10.  Electroplating  with  Copper  ...................................  35 

11.  The  Electro-Chemical  Equivalent  of  a  Metal  ....................  36 

12.  The  Electric  Disk  Stove  or  Hot  Plate  ..........................  41 

13.  Cost  of  Operating  and  Efficiency  of  an  Electric  Flat-iron  ........  43 

14.  Boiling  an  Egg  by  Means  of  Electricity  ........................  46 

15.  The  Immersion  Heater  .......................................  49 

16.  Making  Cocoa  and  Candy  with  the  Aid  of  Electricity  ..........  49 

17.  Testing  a  Nodon  Valve  with  Dry  Cells  .........................  55 

18.  Testing  a  Nodon  with  a  Direct-current  Service  Line  .............  56 

19.  Testing  a  Nodon  Valve  with  Alternating  Current  ..............  57 

20.  Efficiency  Test  of  a  Nodon  Valve  ............................  58 

21.  Efficiency  Test  with  Two  Nodon  Valves  in  Series  ..............  59 

22.  Puncturing  the  Insulating  Wall  of  a  Nodon  Valve  ..............  59 

23.  Efficiency  Test  of  a  Commercial  Electrolytic  Rectifier  ..........  62 

3 


ARGUMENT 


THE  Weston  Monographs  were  prepared  with  the  definite 
object  in  view  of  attempting  to  co-operate  with  and 
assist  science  teachers  in  high  schools  and  collegiate 
preparatory  schools  throughout  this  country. 

Their  context  is  exclusively  on  electrical  subjects;  and  each 
deals  with  a  particular  theme. 

For  instance  B-l  dwells  upon  the  manifest  advantages  of 
training  students  engaged  in  laboratory  work  by  means  of  stand- 
ard apparatus,  such  as  they  will  encounter  in  practical  work 
after  graduation.  It  also  calls  attention  to  the  fact  that  it  is 
inconsistent  as  well  as  unwise  to  attempt  to  perform  modern  pro- 
gressive laboratory  work  by  means  of  antiquated  and  obsolete 
apparatus.  It  shows  what  should  be  done. 

B-2  contains  a  series  of  simple  yet  exceedingly  instructive 
experiments,  and  presents  suggestions  that  should  be  of  great 
value  in  the  preparation  or  amplification  of  an  electrical  course. 
It  tells  what  could  be  done. 

B-3  briefly  describes  several  standard  high  grade  and 
thoroughly  reliable  instruments,  economical  in  price  and  par- 
ticularly adaptable  to  high-school  work. 

In  this  Monograph  B-4,  we  have  compiled  interesting  and 
important  data  which  will  indicate  some  of  the  experiments 
which  are  actually  being  performed  in  progressive  High  Schools 
in  these  United  States.  We  accomplished  this  by  reproducing 
the  actual  work  of  students  without  revision  or  alteration, 
together  with  sketches,  data-sheets,  reports  and  instructors' 
comments,  as  well  as  apparatus  actually  used. 

We  desire  to  explain  as  briefly  as  possible  how  B-4  has  been 
produced. 

Early  in  the  Fall  of  1913,  we  issued  a  letter  to  over  7000 
science  teachers  on  our  list,  in  which  we  directed  attention  to 

5 


6  ARGUMENT 

the  Monographs  we  had  already  issued,  and  requested  sugges- 
tions relating  to  experiments  in  electrical  measurements  which 
they  would  like  to  see  embodied  in  future  Monographs.  We 
were  immediately  deluged  with  replies,  and  as  soon  as  it  was 
feasible  we  began  preparing  data  relating  to  the  experiments 
most  in  demand. 

We  then  conceived  the  idea  of  asking  science  teachers  to 
furnish  us  with  these  experiments,  instead  of  preparing  them 
ourselves;  and  wrote  to  a  number  of  those  who  were  fortunate 
enough  to  possess  a  modern  equipment,  inviting  them  to  con- 
tribute some  specified  exercises. 

In  this  manner  we  hoped  to  fulfill  the  requests  of  science 
teachers  by  publishing  the  work  of  other  science  teachers. 

The  experiments  offered  are  reproduced  verbatim;  but  we 
have  in  some  instances  either  simplified  or  elaborated  connec- 
tion diagrams.  Otherwise  the  authority  for  the  execution  of 
the  work  is  vested  in  the  contributor  cited.  Necessarily  there 
was  much  repetition,  and  it  obviously  became  practicable  to 
print  only  a  few  of  the  contributions  we  received;  but  we  desire 
to  gratefully  acknowledge  the  assistance  of  those  teachers  whose 
work  is  not  incorporated  in  this  Monograph.  Their  tests  were 
of  great  value  to  us,  and  in  many  cases  it  was  exceedingly  difficult 
to  make  a  choice. 

Entirely  aside  from  their  intrinsic  pedagogical  value,  the 
majority  of  these  experiments  have  a  significance  which  cannot 
fail  to  arrest  the  attention  of  the  progressive  instructor.  They 
prove  conclusively  that  the  trend  of  physics  teaching  is  toward 
the  practical  application  of  fundamental  principles. 

They  indicate  also  that  laboratory  work  requiring  the  use 
of  instruments  of  precision  may  be  successfully  performed  by 
young  students  of  either  sex. 

In  conclusion  we  desire  to  direct  special  attention  to  the 
Nodon  Valve  and  Rectifier  experiments;  because  they  are  not 
only  of  the  greatest  interest  pedagogically,  but  since  they  also 
possess  utilitarian  properties,  in  that  they  indicate  how  a  teacher 
who  has  only  alternating  current  service  available,  may  easily 
and  cheaply  transform  to  direct  current;  and  thereby  open  up  a 
greater  realm  of  electrical  experiments  specially  suited  to  the  High 
School  Laboratory. 

WESTON  ELECTRICAL  INSTRUMENT  COMPANY. 


GENERAL   LABORATORY  WORK 


IN  preparing  the  minds  of  beginners  in  experimental  electrical 
work,  and  in  directing  their  attention  to  the  ethical  as  well  as 
the  material  considerations  involved,  it  would  be  to  their  advan- 
tage to  hear  the  following  comments,  which  are  adapted  from  an 
introduction  to  a  loose  leaf  manual  in  Electrical  Measurements. 
We  are  indebted  to  their  author,  Prof.  James  Theron  Rood, 
Ph.D.,  of  Lafayette  College,  for  permission  to  use  them. 

I.     PREPARATION   FOR  LABORATORY  WORK 

A  well-trained  experimenter,  in  any  department  of  science, 
may  at  once  be  known  by  his  ability  to  make  clear,  concise  state- 
ments of  the  laws  and  phenomena  of  that  department  in  which 
he  is  especially  interested. 

An  electrical  laboratory  is  a  place  designed  to  help  men  to 
acquire  such  characteristics,  but  it  is  of  value  to  any  man  only 
in  proportion  as  he  approaches  his  work  therein  with  the  proper 
spirit,  imbued  with  the  desire  to  do  and  learn.  The  first  requis- 
ite is  to  come  to  the  laboratory  knowing  fully  what  you  are  to 
do,  and  how  you  are  to  do  it.  Read  in  advance  the  direction 
sheets  for  the  given  experiments,  look  up  the  references,  be 
prepared  to  get  the  most  out  of  your  performance  of  the  given 
experiment.  If  you  do  not  come  so  prepared,  you  are  almost 
sure  to  become  confused  as  to  what  must  be  done  and  as  to  the 
order  which  must  be  followed.  Required  observations  are  likely 
to  be  omitted,  time  may  be  wasted  on  useless  readings,  interest- 
ing and  valuable  phenomena  may  escape  your  attention  or  be 
wrongly  interpreted,  and  you  may  finish  with  a  confused  instead 
of  a  clear  conception  of  the  method  and  the  value  of  the  test. 
Make  yourself  master  of  the  experiment,  in  the  preparation  for 
it,  in  the  performance  of  it,  and  in  the  writing  of  the  report 

7 


8  GENERAL  LABORATORY  WORK 

about  it.     The  students  who  must  continually  run  to  an  instruc- 
tor for  direction  and  advice  can  never  rise  very  far. 

II.     PERFORMING   THE  EXPERIMENT 

No  general  advice  or  directions  can  be  given  which  will  cover 
each  and  every  experiment.  Each  test  brings  its  own  peculiar- 
ities, its  own  difficulties;  but  there  are  invariably  certain  things 
which  mark  the  trained  and  careful  experimenter.  Some  of  these 
are  given  in  what  follows: 

III.     APPARATUS 

All  apparatus  used  in  testing  should  be  most  carefully 
handled.  What  company  would  retain  an  employee  who  mis- 
used its  instruments  or  machines? 

Accidents  may  happen  to  even  the  most  careful  experi- 
menters, but  whenever  they  do  occur,  they  should  be  reported 
at  once.  Placing  the  injured  instrument  back  in  its  place  without 
reporting  its  injury  is  the  work  of  a  sneak.  Such  action  may 
result  in  the  apparatus  remaining  unrepaired  until  a  time  when 
a  co-worker,  needing  the  apparatus  for  immediate  use,  discovers 
that  it  is  injured  and  that  it  may  have  to  be  sent  away  for 
repairs.  He  is  thus  kept  back  in  his  work  when,  had  the  injury 
been  known,  suitable  repairs  might  have  been  made  before  the 
apparatus  was  again  needed. 

IV.     DIAGRAMS 

Before  beginning  any  experiment,  make  a  clear  diagram 
of  the  proper  arrangement  of  all  circuits  to  be  used,  with  all 
connections,  instruments,  resistors,  switches,  cut-outs,  etc., 
shown  by  the  conventional  symbols.  Use  heavy  lines  for 
indicating  conductors  carrying  large  currents,  such  as  electric 
power  service  wires,  bus-bars,  feeders  for  motors,  etc.,  and 
light  lines  for  potential  circuits,  such  as  leads  to  the  e.m.f. 
terminals  of  wattmeters,  voltmeters,  etc.  Submit  this  diagram 
to  the  instructor  for  his  criticism  and  approval.  Then  connect 
up  according^  to  this  diagram.  Make  no  changes  in  it  without 
the  approval^of  the  teacher. 


GENERAL  LABORATORY  WORK 


V.     INSTRUMENTS 

Almost  without  exception,  all  makes  of  ammeters  have  un- 
insulated, metal  binding-posts,  while  voltmeters  have  posts 
encased  in  insulation.  The  two  kinds  of  meters  can  thus  be 
at  once  told  apart.  Milli voltmeters  are  frequently  used  as 
ammeters  by  connecting  shunts  in  the  line,  the  potential  drop 
across  these  shunts  being  proportional  to  the  current;  the  read- 
ings of  the  meter  when  its  leads  are  placed  across  the  terminals 
of  the  shunt  will  be  proportional  to  the  current  flowing,  and 
may  be  read  directly  in  amperes.  When  so  used  the  values 
of  the  scale  divisions  of  the  meter  will  depend  upon  the  partic- 
ular shunt  used  as  well  as  upon  the  meter  leads.  Each  milli- 
voltmeter  must  always  be  used  both  with  its  own  shunt  and  its 
own  leads.  The  shunt  is  always  connected  in  the  line  and  the 
milli voltmeter  across  the  shunt.  Remember,  ammeters  go  in 
the  line,  voltmeters  go  across  the  line.  Never  lay  instruments 
on  the  floor  or  on  a  chair.  Always  put  them  on  a  table  and 
then  pass  the  wires  through  holes  in  the  edge  of  the  table  or  else 
so  fasten  them  that  there  can  be  no  chance  of  an  instrument 
being  pulled  down  onto  the  floor.  If  any  instrument  has  a  zero 
error  reading,  allow  for  it  in  your  readings,  or  have  it  reset  by 
means  of  its  zero  adjusting  device.  NEVER  OPEN  OR  CLOSE  A 
CIRCUIT  AT  ANY  AMMETER  BINDING  POST.  Trace  out  the  polarity 
of  any  D.C.  circuit  before  connecting  in  an  instrument.  Be 
sure  that  the  current  flows  through  the  instrument  in  the  right 
direction.  If  it  does  not,  OPEN  THE  CIRCUIT  BEFORE  REVERSING 

ANY     AMMETER     LEADS.      REVERSE     VOLTMETER     LEADS     AT      THE 

CIRCUIT  END,  NOT  AT  THE  METER.  Read  all  meters  to  one-tenth 
of  the  smallest  division.  Look  for  any  parallax  when  making 
a  reading. 

VI.     ORDERLINESS 

During  the  performance  of  all  tests,  see  that  all  instruments, 
switches,  lines,  etc.,  are  kept  in  an  orderly  condition  and  not 
allowed  to  become  a  confused  maze.  After  finishing  an  experi- 
ment, see  that  all  instruments,  rheostats,  lamps  and  other  pieces 
of  apparatus  are  replaced  in  their  proper  places  in  their  cases. 

Coil  up  and  put  away  all  lengths  of  wire.     Put  everything 


10          GENERAL  LABORATORY  WORK 

back  in  its  place  and  leave  the  apj  I  3  as  weO  as  all  the  tables, 
etc.,  free  from  all  \\ires  and  in  perfect  order  ready  for  the  next 
users.  When  finished,  replace  covers  on  all  motors  or  dynamos 
used.  Next  to  success  in  the  performance,  orderliness  in  the 
handling  of  laboratory  apparatus  is  the  most  important  thing 
to  be  learned  in  a  laboratory.  Your  care  in  this  respect  will  be 
considered  in  determining  your  term  grade. 

VH.     REPORTS 

To  be  able  to  write  a  satisfactory  report  of  an  investigation 
is  an  art  and  accomplishment  that  should  be  the  desire  and  pride 
of  every  engineer,  in  even*  walk  of  science.  It  is  the  keystone 
of  all  science.  In  its  essence,  an  engineer's  report  is  a  why. 
a  what,  a  how.  a  this  and  a  therefore. 

A  good  engineer  must  have  knowledge,  judgment  and  common 
sense.  The  laboratory,  rightly  used,  is  the  best  place  for  the 
development  of  such  powers,  and  should  be  valued  as  such. 

Let  your  laboratory  motto  be: 

WORK  -OBSERVE  —THINK 


EXPERIMENTAL  ELECTRICAL  TESTING 


EXPERIMENT  NO.  1 

RESISTANCE   MEASUREMENTS 

The  following  experiments  were  selected  from  a  number 
kindly  contributed  by  Mr.  William  F.  Evans,  Instructor  in 
Physics,  Girls'  High  School,  Brooklyn,  N.  Y. 

They  are  copied  from  the  laboratory  note-book  of  the  girl 
who  did  the  work. 

A  modification  of  these  methods  is  used  in  shop  practice 
for  a  preliminary  measurement  of  resistance  wires  in  course 
of  manufacture.  To  eliminate  errors  due  to  a  variation  in  cur- 
rent, the  wire  and  the  rheostat  are  both  connected  with  one 
pole  of  the  cell,  and  a  double-throw  switch  is  used,  so  that  the 
at  may  be  adjusted  until  the  same  deflection  Is  obtained 
when  current  is  passed  through  either  circuit  in  rapid  succession. 
Reference,  "  Laboratory  Exercises."  Fuller  and  Brownlee,  page 
270. 

Resistance  of  a  Conductor  by  the  Substitution  Method 

Apparatus.  Weston  ammeter:  dry  cell;  rheostat,  50  cm., 
No.  30  German  silver  wire;  and  leads. 

(1)  Connect   up  the   cell,   the   ammeter  and  the   unknown 
resistance  in  series,  being  sure  that  all  contacts  are  dean  and  all 
connections  tight.     See  Fig.  1. 

(2)  Substitute  the  resistance  box   (with  all  plugs  removed) 
for  the   unknown   resistance   and  then   decrease  the   resistance 
of  the   circuit   until  the   current   is  the   same  as  before.    See 
Fig.  2. 

(3)  What  then  is  the  resistance  of  the  50  cm.  No.  30  G    - 


11 


12 


EXPERIMENTAL  ELECTRICAL  TESTING 


STUDENT'S  REPORT 

(1)  I   connected  up  as  in  diagram  the   cell,   the   ammeter, 
and  the  unknown  resistance  (50  cm.  No.  30  German  silver  wire), 


FIG.  1. — RESISTANCE  MEASUREMENTS.     (Reproduced  from  Student's  Sketch.) 

Evans'  Method. 
Instrument  Used  is  a  Model  280,  Weston  Ammeter.     Range  5  Amperes. 

being  sure  that  all  contacts  were  clean  and  all  connections  tight. 
6  amperes. 

(2)  I  substituted  the  resistance  box  for  the  unknown  resist- 
ance with  all  plugs  out,  and  reduced  the  resistance  of  the  cir- 


C 


FIG.  2. — RESISTANCE  MEASUREMENTS.     (Reproduced  from  Student's  Sketch.) 

Evans'  Method. 
Instrument  Used  is  a  Model  280,  Weston  Ammeter.     Range  5  Amperes. 

cuit  by  putting  in  plugs  until  the  reading  of  the  ammeter  was 
the  same  as  before — 1.8  ohms. 


COMPARATIVE  RESISTANCES  OF  CONDUCTORS        13 


(3)  The  resistance  then  of  50  cm.  of  No.  30  G.  S.  wire  is 
1.8  ohms,  because  the  reading  was  the  same  when  the  resist- 
ance box  was  connected  as  when  the  German  silver  wire  was 
connected. 

EXPERIMENT  NO.  2 
COMPARATIVE   RESISTANCES   OF   CONDUCTORS 

Apparatus.  As  in  preceding  experiment;  together  with 
other  wires  of  various  sizes. 

OBSERVATIONS 


Length  of  Conductor. 

Area  of 
Cross-section  . 

Amp. 

Ohms. 

(1) 

Varying  Lengths 

(1)    50  cm.  G.  S.  wire 
(2)  100  cm.  G.  S.  wire 
(3)  150  cm.  G.  S.  wire 

.05  sq.mm. 
.05  sq.mm. 
.05  sq.mm. 

.60 
.32 
.20 

1.8 

3.4 
.6 

(2) 
Varying  Areas  .  .  . 

(1)  50  cm.  G.  S.  wire 
(2)  50  cm.  G.  S.  wire 
(3)  50  cm.  G.  S.  wire 

.05  sq.mm. 
.  10  sq.mm. 
.  15  sq.mm. 

.60 
1.04 
1.34 

1.8 
.8 
.5 

(3) 
Varying  material  . 

(1)  50  cm.  G.  S.  wire 
(2)  50  cm.  brass  wire 
(3)  50  cm.  copper  wire 

.05  sq.mm. 
.05  sq.mm. 
.05  sq.mm. 

.65 
2.28 
3.70 

1.9 
.3 
.1 

Description.  I  connected  up  the  German  silver  wire  as  in 
preceding  experiment.  Then  I  substituted  the  resistance  box 
as  in  preceding  experiment.  First  I  used  50  cm.,  then  100, 
last  150  cm.  of  German  silver  wire.  Next  I  used  wire  with 
.05  sq.  mm.  cross  section;  then  10  sq.mm.,  finally,  15  sq.mm. 
After  this  I  used  50  cm.  of  brass  and  50  cm.  of  copper  wire  in 
place  of  the  German  silver  wire. 
March  21,  1913. 

EXPERIMENT  NO.  3 
CONSTRUCTING  AND  TESTING  A  LAMP    BANK  RHEOSTAT 

In  commercial  work,  adjustable  rheostats  are  extensively 
used;  in  fact  they  are  indispensable  when  current  from  service 
lines  is  employed  for  experimental  purposes. 

For  precision  tests  in  laboratories,  rheostats  that  are  non- 


14  EXPERIMENTAL  ELECTRICAL  TESTING 

inductive  and  which  have  a  negligible  temperature  coefficient 
are  preferable  and  often  necessary,  but  in  general  commercial 
testing  adjustable  lamp  bank  rheostats  are  most  in  demand  for 
current  regulation,  or  for  building  up  a  load. 

The  rheostat  described  in  this  experiment  should  appeal 
to  the  science  teacher  because  it. is  simple  in  construction  and 
yet  permits  a  wide  range  of  adjustment  owing  to  the  ingenuity 
of  its  designer. 

This  rheostat  was  designed  by  Charles  P.  Rockwell,  and 
constructed  by  him  with  the  assistance  of  Gordon  R.  Milne, 
Barringer  High  School  students,  Newark,  N.  J.  The  tests 
made  with  it  are  their  joint  work. 


FUSES 


FIG.  3. — A  Complex  Lamp  Bank. 


Following  is  their  own  description: 

This  board  was  designed  to  allow  any  number  of  lamps, 
up  to  twelve,  to  be  connected  in  multiple,  series,  or  multiple 
series. 

An  oak  board  was  obtained  from  the  school  shop.  Accord- 
ing to  plan,  a  Perkins  25  amp.  double-pole  single-throw  switch 
and  a  fuse  block  were  placed  at  the  extreme  right,  four  Perkins 
single  throw,  single-pole  switches  were  placed  next  to  these,  two 
for  ingoing  and  two  for  returning  current.  Two  other  Perkins 
switches  placed  next  allowed  current  to  cross  over  to  different 
banks  of  lamps.  Twelve  sockets  wTere  screwed  at  equal  dis- 
tances from  each  other. 


TESTING  A  LAMP  BANK  EHEOSTAT 


15 


The  small  cut-out  switches  were  made  by  bending  copper 
strips  into  jaws  for  receiving  copper  strips  as  blades.  Holes 
were  bored  to  receive  jaws  which  were  sealed  in  place  with  seal- 
ing wax. 

Connections  were  made  and  lamps  were  screwed  in  as  shown 
in  Fig.  3. 


APPARATUS  AND  MATERIALS  REQUIRED 


195 

WATTS  < 


-OCh 

OO 

00 
OO- 


128 
WATTS 


256 

WATTS 


1  Weston  voltmeter. 
1  W^eston  ammeter. 
1  portable  testing  set. 
1  oak  board  18X40  ins. 
1  Perkins  knife  switch, 
25  amp.,  double  pole,  single 
throw. 

^[6  Perkins  knife  switches, 
25  amp.,  single  pole,  single 
throw. 

Sheet  copper  for  mak- 
ing 27  switches   (jaws   and 
blades)    which   may    be   replaced   with 
single-throw  switches. 

1  Edison  double-plug  cut-out. 

12  Bryant  porcelain  receptacles,  keyless. 

12  carbon  filament  32 
C.P.  lamps. 

2  fuses,  mica  cap,  15 
amp. 

15  ft.  No.  14  (B.  &  S. 
gauge)  bare  copper  wire. 

DIRECTIONS    FOR    OPE- 
RATING  AND  TESTING 


FIG.  4. 
Trumbull    single-pole, 


122 
WATTS 


ooo 
ooo 
ooo 


162 
>WATTS 


FIG.  5. 


IV,   V,  VI,  VII,  VIII. 
T,  Uy  V,  W,  X. 


NOTE.     All   switches 
not  specified  closed  must 
be  open.     For  all  lamps 
in  multiple:     Close  III, 
C,  D,  E,  F,  G,  H,  K,  L,  M,  N,  0,  P,  S, 


16 


EXPERIMENTAL  ELECTRICAL  TESTING 


For  all  lamps  in  series.  Close  III,  VI,  IX.  A,  F,  I,  K, 
Q,  V,  W,  P,  G. 

FOR  MULTIPLE  SERIES  GROUPING 

Three  groups  in  series,  each  group  containing  four  lamps 
in  multiple.  Close  all  except  IV,  if,  VII,  VIII,  IX. 

Two  groups  in  series,  each  group  containing  four  lamps  in 
multiple.  Close  all  except  III,  V,  VII,  VIII,  IX. 


-oooo- 
oooo 


57 
WATTS 


FIG.  6. 
ARRANGEMENT 


Multiple 
Watts. 

No.  of 
Lamps. 

Series 
Watts. 

MULTIPLE  SERIES.     See  Fig.  4 

Watts. 

Groups  of 

No.  in  Mult. 

124 
248 
368 
485 
585 
695 
845 
955 
1080 
1197 
1310 
1420 

1 

2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 

125 
60 
37.5 

27 
20 
15 
12.5 
10 
8 
7 
6 
5 

2  in  series 
2  in  series 
2  in  series 

2  in  mult. 
3  in  mult. 
4  in  mult. 

128 
195 
256 

MULTIPLE  SERI 

3  in  series 
3  in  series 
3  in  series 

ES.     See  Fig.  5 

2  in  mult. 
3  in  mult. 
4  in  mult. 

80 
122 
162 

MULTIPLE  SERI 

4  in  series 
4  in  series 
4  in  series 

ES.    See  Fig.  6 

2  in  mult. 
2  in  mult. 
3  in  mult. 

57 
60 

85 

WATTS  PER  LAMP  IN  ABOVE  ORDER  1st  COLUMN 


Lamp  No  

1 

2 

3 

4 

5  I  •  6  1  7  .   8 

[ 
9   i  10  i  11 

,2 

Watts  

124 

124 

120 

120 

100   110   150  1  110 

135  i  118  1  113 

1 

110 

TEST  OF  FUSES 
RESISTANCE  PER  LAMP 


17 


Lamp  No. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

Res  

Hot 

112 

112.2 

116 

116 

139.2 

126.3 

124.2 

126.3 

118.8 

118.0 

123.2 

126.3 

Res  

Cold 

225 

230 

240 

230 

235 

235 

230 

245 

225 

242 

235 

240 

R  (hot)  was  when  filaments  were  incandescent. 


V2 
Formula  used  R  —  ~=    or 


R 


1182 
W  ' 


R  (cold)  was  when  lamps  were  at  room  temperature  (22° 
C.).  Results  were  obtained  by  measurement  with  a  portable 
testing  set. 

EXPERIMENT  NO.  4 
TEST   OF  FUSES' 

From  Lafayette  College,  Department  of  Electrical  Engineering,  Labora- 
tory Direction  Sheets.  Available  through  the  courtesy  of  the  author, 
Professor  J.  T.  Rood. 

References:  Barr,  Direct  Cur.  Elec.  Eng.,  p.  479;  Swenson  and  Franken- 
field,  Vol.  I,  p.  342;  Standard  Handbook  for  Elec.  Engs.,  p.  585;  Foster's 
Handbook,  pp.  217,  1275. 

Purpose.  Every  electric  circuit  should  be  provided  with 
some  form  of  apparatus  designed  to  prevent  the  flow  of  any 
excessive  current  which  might  start  a  fire  or  burn  out  any  appa- 
ratus. The  insurance  companies  require  that  all  lighting  and 
motor  circuits  shall  be  so  fused  or  protected  that  the  current- 
carrying  wire  shall  never  be  overheated.  Such  protective  devices 
are  called  cut-outs.  They  may  be  pu  tinto  two  classes,  fuses  and 
circuit  breakers.  Fuses,  according  to  their  arrangement,  may 
be  divided  into  three  classes,  open,  expulsion  and  enclosed. 
Circuit  breakers  are  somewhat  more  convenient,  but  are  much 
more  costly  and  occupy  more  space.  They  are  better  for  cir- 
cuits carrying  large  current,  or  where  the  circuit  is  liable  to  be 
opened  or  overloaded  frequently,  since  they  are  more  sure  of 
opening  the  circuit. 

Construction.  Fuses  are  merely  strips  of  metal  of  such 
shape  and  material  as  will  fuse  or  "  blow  "  before  any  excess 
current  can  flow  for  any  length  of  time.  The  I.  R.  losses  in  the 


18  EXPERIMENTAL  ELECTRICAL  TESTING 

metal  due  to  the  current  passing  causes  the  strip  to  become 
heated.  If  the  heat  is  generated  faster  than  it  can  be  radiated, 
the  fuse  material  melts  and  the  circuit  is  thus  opened,  provided 
the  arc  does  not  hold  between  the  terminals  of  the  fuse  block 
on  account  of  the  metallic  vapor  which  may  be  left  in  the  air 
between  them.  This  limits  the  amount  of  current  which  a 
given  fuse  can  safely  break,  unless  there  is  provided  some  means 
of  expelling  the  hot  vapor  (expulsion  fuses),  or  of  condensing 
it  (enclosed  fuses).  In  this  last  the  vapor  is  supposed  to  be 
immediately  condensed  in  the  spaces  between  the  granules  of 
the  non-inflammable,  non-conducting  material  which  fill  the 
tubes.  On  account  of  the  variation  of  the  alloy  in  the  different 
parts  of  the  fuse  wire,  as  well  as  on  account  of  the  effect  of  air 
currents,  open  fuses  cannot  be  depended  upon  to  always  blow 
at  the  same  current  with  the  same  length  and  diameter  of  fuse 
wire.  For  open  fuses  alloys  of  lead,  antimony  and  bismuth 
are  mostly  used.  Enclosed  fuses  are  mostly  of  zinc.  For  large 
fuses  copper  is  sometimes  used,  but  it  is  liable  to  hold  the  arc 
through  its  vapor. 

Object.  The  object  of  this  experiment  is  to  test  some 
commercial  fuse  wire  and  to  determine  the  relation  (a)  between 
length  and  the  fusing  current  (6)  between  diameters  for  this 
last,  all  diameters  of  wires  tested  should  be  of  the  same  make) , 
(c)  to  investigate  the  construction  and  action  of  some  types  of 
enclosed  fuses. 

Apparatus.  Various  diameters  of  fuse  wires,  fuse  block 
with  adjustable  terminals,  adjustable  resistor,  Weston  ammeter 
and  inch  scale,  also  line  switch. 

Part  I.  Set  the  terminals  of  the  fuse  block  1J  inches  apart 
in  the  clear  and  insert  a  length  of  fuse  wire.  Connect  the 
fuse  block  in  series  with  the  ammeter,  adjustable  resistor  and 
switch;  and  connect  the  whole  across  the  D.C.  supply  circuit. 
See  that  the  resistance  is  set  to  allow  only  a  small  current  to 
flow,  close  the  switch  and  slowly  increase  the  current  until  the 
fuse  blows.  Repeat  with  the  same  size  of  wire  for  fuse  lengths 
of  2,  2J,  3,  and  3J  inches.  Repeat  this  series  for  all  the  dif- 
ferent diameters  of  wire  given  you.  Record  make  of  wire,  rated 
capacity,  and  blowing  current.  Calculate  and  record  the  per- 
centage ratio  between  the  rated  capacity  and  the  blowing  cur- 
rent. Note  carefully  the  construction  of  each. 


THE  FUSING  EFFECT  OF  AN  ELECTRIC  CURRENT     19 

Report.  Describe  what  you  did.  Plot  curves  showing  (a) 
relation  between  length  and  fusing  current  for  wires  tested, 
(6)  relation  between  diameter  and  fusing  current  for  a  given 
length  of  fuse.  The  form  of  curve  for  this  last  is  usually: 

*-(//««)*, 

where    d  =  diameter  of  wire ; 
/  =  fusing  current,  and 

a  =  constant  depending  on  the  composition  of  the  wire. 
Give  good  sketches  of  the  construction  of  the  enclosed  fuses 
tested  and  give  description  of  the  details  of  each. 

Questions,  (a)  Do  you  think  the  size  or  mass  of  the  ter- 
minals of  the  fuse  block  can  affect  the  value  of  the  fusing  current? 

(b)  If,  so,  how? 

(c)  Would  this  effect  be  proportional  for  all  lengths  of  the 

fuse  wire?     Why? 

Why  should  the  current  in  every  case  be  increased  slowly? 
Why  should  the  enclosed  fuses  be  given  a  preliminary 

heating  before  being  blown? 


EXPERIMENT  NO.  5 
THE   FUSING   EFFECT   OF  AN   ELECTRIC   CURRENT 

The  following  experiment  on  fuses  was  supplied  by  Mr. 
Milton  M.  Flanders  of  the  Bliss  Electrical  School,  Takoma 
Park,  Washington,  D.  C.  It  is  so  clean-cut  and  practical  that 
comments  are  superfluous.  Sketch  is  a  reproduction  of  the  one 
sent  in  by  the  students  performing  the  test. 

TEST  NO.  A-400 

HEAT 
A  study  of  the  fusing  effect  of  an  electrical  current. 

OBJECT  OF  TEST 

To  determine  the  current  and  time  required  to  melt  fuses 
under  'various  conditions. 


20 


EXPERIMENTAL  ELECTRICAL  TESTING 


APPARATUS  REQUIRED 


1  ammeter  (0-100) 
1  rheostat 
1  stop  watch 
1  thermometer 


Various  fuses 
1  circuit  breaker 
1  switch 
Connecting  wires 


CONDUCT  OF  TEST 

I.  Preparation.     Set  up  the  apparatus  as  per  diagram,  con- 
necting to  a  source  of  low  potential  and  high  current,  as  a  stor- 


CIRCUIT  BREAKER 


AMMETER 


FIG.  7. — STUDY   OF   THE   FUSING    EFFECT   OF   AN   ELECTRICAL   CURRENT. 
(Reproduced  from  Students'  Sketch.)     Flanders'  Method. 

Instrument  Used  was  a  Model  1,  Weston  Ammeter.     Range  100  Amperes. 

NOTE. — For  all  ordinary  laboratory  work,  fuses  that  will  "  blow  "  at  1 
to  20  amperes  will  suffice,  and  an  ammeter  of  lower  range  than  the  above 
will  be  preferable. 

age  battery.  Close  switch  S  and  after  inspection  by  instructor, 
admit  current  and  correct  polarity  of  ammeter  if  necessary. 
See  Fig.  7. 

II.  Operation,  (a)  Admit  current  to  200  per  cent  rating 
of  fuse  under  test,  holding  this  constant  by  means  of  the  rheo- 
stat R.  Open  switch 'S  and  simultaneously  start  stop-watch. 
Note  the  exact  time  required  for  the  fuse  to  open  the  circuit. 
Repeat  at  least  three  times. 

(6)  Repeat  above  with  different  fuses,  as  directed. 

(c)  Repeat  above  on  increasing  current,  the  rate  of  increase 
being  1  ampere  per  minute,  and  tabulate  results. 


THE  FUSING  EFFECT  OF  AN  ELECTRIC  CURRENT     21 


(d)  Repeat  operation  (a)  with  the  fuse  wire  in  contact  with 
some  foreign  insulating  substance. 

(e)  Repeat  operation   (a),   first  raising  temperature  of  fuse 
50°  C.,  by  means  of  a  heating  chamber. 

III.  Calculation.     Tabulate    all   results    as    indicated    below: 


Fuse. 

Wire.          Length. 

Deg.  C. 

Rating. 

Amps. 

Time. 

Note. 

Link 

Shawmut     1.625 

17.8 

6 

12 

10 

11 

11 

Avg.l0.66+ 

REPORT  ON  TEST  No.  A-400 

Instrument  used:  Weston  Model  1,  Ammeter  No.  5378.     Centigrade  Ther- 
mometer No.  3. 

DATA 

OPERATION  (a) 


Type. 

Wire. 

Length. 
Ins. 

Temp. 
Deg.  C. 

Rating, 
Amps. 

Amps. 

Time,  Sec. 

Remarks. 

Daum 
Damn 

Shawmut 
Shawmut 

1.625 

1.625 

22 

22 

6 
6 

12 
12 

8.6 

7.2 

Average 
Time 

Daum 

Shawmut 

1.625 

22 

6 

12 

10.0 

8.93+  sec. 

OPERATION  (6) 


Type. 

Wire. 

Length. 
Ins. 

Temp. 
Deg.  C. 

Rating, 
Amps. 

Amps. 

Time,  Sec. 

Remarks. 

Link 
Link 

Shawmut 
Shawmut 

1.625 
1.625 

17.8 
17.8 

6 

6 

12 
12 

10 

11 

Average 
Time 

Link 

Shawmut 

1.625 

17.8 

6 

12 

11 

10.66+sec. 

OPERATION  (c) 


Type. 

Wire. 

Length, 
Ins. 

Temp. 
Deg.  C. 

Rating, 
Amps. 

Amps. 

Time.  Sec. 

Remarks. 

Daum 

Shawmut 

1.625 

21 

6 

12 

12  min. 

4  sec. 

Daum 

Shawmut 

1.625 

21 

6 

10 

9  min.  20  sec. 

Daum 

Shawmut 

1.625 

21 

6 

10 

9  min.  12  sec. 

22  EXPERIMENTAL  ELECTRICAL  TESTING 

OPERATION  (</) 


T   pe. 

Wire. 

Length. 
Ins. 

Temp. 
Deg.  C. 

Rating, 
A  mps. 

Amps. 

Time.  Seo. 

Remarks. 

Link 
Link 

Shawmut 
Shawmut 

1.625 
1.625 

17.8 
17.8 

6 
6 

12 

12 

21 
19 

Average 
Time 

Link 

Shawmut 

1.625 

17.8 

c,  - 

12 

22 

20.66+  sec. 

NOTE. — In  operation  (d)  the  fuse  wire  was  in  contact  with   a    marble 
block  for  .75  in.  of  its  length. 

OPERATION  (e) 


Type. 

Wire. 

Length. 
Ins. 

Temp. 
Deg.  C. 

Rating, 
Amps. 

Amps. 

Time,  Sec. 

Remarks. 

Link 

Shawmut 

1.625 

49 

6 

12 

8.2 

Average 

Link 

Shawmut 

1.625 

49 

6 

12 

7.2 

Time 

Link 

Shawmut 

1.625 

49 

6 

12 

8.0 

7.8  sec. 

NOTE. — None  of  the  above  fuses  would  blow  at  rated  current  and  normal 
temperature  of  surrounding  air. 

Above  test  performed  by  F.  G.  Shipley  and  L.  T.  Petit. 

Instrument  repairs  are  expensive ! 

Fuses  are  cheap ! 

Why  not  insist  that  students  insert  a  fuse  between  the  load 
and  the  ammeter  in  all  tests,  so  that  the  ammeter  cannot  be 
burned  out  or  overlo  ded? — Compiler's  Note. 


INDUCTION 

We  requested  Mr.  Geo.  M.  Turner  of  the  Department  of 
Physics  and  Chemistry,  Hasten  Park  High  School,  Buffalo, 
N.  Y.,  to  contribute  some  exercises  on  Induction,  because  the 
effects  due  to  induction  must  often  be  taken  into  consideration 
in  the  designing  or  use  of  commercial  apparatus  in  order  to 
obtain  efficient  results.  In  this  respect,  the  effect  of  induction 
may  be  beneficial  or  harmful,  but  a  knowledge  of  this  phenome- 
non is  always  necessary  before  a  student  can  make  any  progress 
in  acquiring  even  an  elementary  knowledge  of  electrical  measure- 
ments. 


INDUCTION  23 

Mr.  Turner  intends  to  include  the  following  experiments 
in  his  physics  course  and  writes  concerning  them  as  follows: 

"  Your  request  for  an  experiment  on  Induction  for  the  forth- 
coming Monograph  received. 

"  It  is  my  understanding  that  you  desire  an  experiment  that 
will  include  the  center-scale  millivoltmeter.  As  my  pupils  have 
not  as  yet  used  this  instrument  for  their  induction  work,  it  would 
be  impossible  to  furnish  any  results  from  their  standpoint. 

"  Recently,  I  used  the  instrument  in  a  series  of  induction 
tests,  such  as  our  high-school  young  people  make,  and  found 
that  while  not  as  sensitive  as  the  ordinary  D'Arsonval  Galvanom- 
eter used  in  high-school  work,  it  was  sufficiently  sensitive  for  such 
experiments  as  our  young  people  would  need  to  do.  The  prompt 
return  of  the  pointer  to  the  zero  reading  and  the  ease  of  watch- 
ing the  scale  made  the  millivoltmeter  seem  much  better  adapted 
for  this  work  than  was  the  galvanometer. 

"  Later  I  tried  the  millivoltmeter  in  connection  with  the 
1  Student-sliding-contact  Wheatstone  Bridge  '  of  the  wire  type. 
With  resistances  about  10  ohms,  the  instrument  was  all  that  could 
be  desired,  admitting  of  the  exact  location  of  the  contact  to 
within  a  millimeter.  With  resistances  about  a  hundred  ohms 
the  instrument  gave  a  width  to  the  neutral  point  of  between  2 
and  3  millimeters.  When  the  resistance  was  increased  to  1000 
to  4000  ohms,  the  neutral  point  was  extended  to  approximately 
10  millimeters.  By  increasing  the  battery  power  for  the  higher 
resistances  from  1  cell  to  3  cells,  the  range  of  the  neutral  point 
was  reduced  to  2  or  3  millimeters  (for  the  4000  ohms). 

'  These  results  indicate  an  amply  sensitive  instrument  for 
such  work  in  the  hands  of  the  high-school  student,  as  his  results 
need  not  vary  as  much  as  1  per  cent.  It  is  very  likely  that  many 
of  the  resistance  boxes,  used  in  the  high-schools,  will  vary  as  much, 
or  more  than  1  per  cent.  Again,  the  prompt  return  of  the  pointer  to 
zero  reading  proved  of  great  assistance,  and  a  marked  time  saver. 

"  In  general,  I  am  very  much  pleased  with  the  results  of  the 
working  of  the  instrument.     It  is  my  intention  to  order  enough 
for  our  laboratory  work  early  next  year. 
"Very  sincerely, 

"(Signed)  GEO.  M.  TURNER. 

"  It  may  be  proper  for  me  to  advise  you  that  the  customary 
(high  school)  slide-wire  bridge  uses  one  meter  of  wire." 


24 


EXPERIMENTAL  ELECTEICAL  TESTING 


EXPERIMENT  NO.  6 
CURRENTS   INDUCED  BY  MAGNETISM 

Object  of  Experiment 

(1)  To  observe  the  effect  of  moving  a  magnetic  pole  into  a 
coil  of  wire. 

(2)  To  compare  the  effect  of  moving  a  magnetic  pole  into 
the  coil  with  that  of  removing  the  pole  from  the  coil. 

(3)  To  observe  the  effect  of  moving  unlike  poles  into  a  coil. 

(4)  To  observe  the  effect  of  moving  the  coil  instead  of  moving 
the  magnet. 

(5)  To  observe  whether  the  induced  current  aids  or  opposes 
the  movement  between  the  coil  and  the  magnet. 


ZERO  CENTER 
MODEL  280 


FIG.  8. — CURRENT  INDUCED  BY  MAGNETISM.     Turner's  Method. 

Instrument  Required  is  Model  280,  Weston  Zero  Center  Milli voltmeter. 
Range  100-0-100  Millivolts. 

APPARATUS 

Weston  milli voltmeter,  with  zero  in  the  center  of  the  scale. 
Coil  of  wire  (50  to  100  turns  of  No.  28  double-cotton  covered 
wire). 

Small  bar  magnet. 

Connecting  wires. 

PROCEDURE 

I 

Preliminary.  Before  making  the  tests  called  for  in  this  exper- 
iment it  is  desirable  to  find  out  the  direction  of  thrust  of  the  milli- 


CURRENTS  INDUCED  BY  MAGNETISM  25 

voltmeter  needle,  when  current  enters  it  by  the  right-hand  bind- 
ing post.  In  order  to  determine  this,  a  thin  strip  of  zinc  may 
be  fastened  to  one  end  of  a  connecting  wire  and  the  other  end 
attached  to  the  left-hand  binding  post  of  the  milli voltmeter. 
With  the  second  wire  attached  to  the  right-hand  binding  post, 
the  zinc  and  copper  ends  of  the  wires  may  be  dipped  in  ordinary 
hydrant  water,  or  (if  this  has  not  enough  conductivity)  into 
hydrant  water  with  a  few  minute  crystals  of  salt  added. 

The  information  gained  by  the  thrust  of  the  needle  under 
these  conditions  serves  as  a  guide  to  the  direction  of  current 
flow  through  the  millivoltmeter  during  the  tests  that  follow. 
Of  course,  current  entering  the  millivoltmeter  by  the  left-hand 
binding  post  produces  a  thrust  of  the  needle  in  a  direction  oppo- 
site to  that  caused  by  current  entering  by  the  right-hand  bind- 
ing post. 

Connect  the  terminals  of  the  coil  to  the  millivoltmeter. 

MANIPULATION 
II 

(a)  While  watching  the  millivoltmeter,  the  North  pole  of 
the  bar  magnet  may  be  thrust  into  the  center  of  the  coil  and 
held  there.  The  movement  of  the  needle,  during  the  movement 
of  the  magnet,  to  left  or  right  is  noted.  See  Fig.  8. 

(6)  Upon  removing  the  North  pole,  a  movement  of  the 
needle  in  a  direction  opposite  to  that  of  the  entering  pole  is 
observed. 

(c)  To  show  that  a  temporary  current  through  the  milli- 
voltmeter is  due  to  the  relative  motion  between  the  coil  and 
magnet,  the  coil  may  be  moved  toward  and  from  the  North  pole 
of  the  magnet,   with  results  similar  to  those  observed  under 
(a)  and  (6). 

(d)  When  the  South  pole,  instead  of  the  North  pole  is  used, 
a  second  series  of  observations  is  obtainable,  which  gives  move- 
ments of  the  needle  opposite  to  those  of  (a),  (6)  and  (c). 

(e)  In  order  to  show  that  the  rate  at  which  the  lines  of  force 
(thrust  out  by  the  magnet)  are  cut  by  the  wire  of  the  coil,  alters 
the  deflection  of  the  needle  (and  hence  the  electro-motive  force 
of  the  current  produced),  the  magnet  may  be  made  to  enter  the 
coil  at  first  slowly,  then  more  rapidly. 


26  EXPERIMENTAL  ELECTRICAL  TESTING 

(/)  After  a  record  has  been  made  of  the  result  of  the  observa- 
tions of  (a),  (b),  (c),  (d),  it  is  quite  possible,  by  use  of  the  pre- 
liminary information,  bearing  upon  the  movement  of  the  milli- 
voltmeter  needle  when  the  current  enters  the  right-hand  binding 
post,  to  find  out  (by  Ampere's  hand  rule)  whether  the  polarity 
of  the  coil  of  wire  is  such  as  to  produce  a  magnetic  pole  that  helps 
or  hinders  the  movement  between  the  coil  and  magnet  in  each 
of  the  trials  (a),  (6),  (c),  (d). 


EXPERIMENT  NO.  7 
CURRENTS    INDUCED    BY    ELECTRO    MAGNETISM 

Object  of  Experiment 

(1)  To  observe  the  effect  in  a  coil  of  wire,  of  moving  another 
coil  of  wire,  through   which  a  current  is  flowing,   toward  the 
former  coil  and  away  from  this  coil. 

(2)  To  observe  the  change  of  effect  when  the  moving  coil  lias 
a  soft  iron  core. 

(3)  To  observe  the  effect  in  a  coil  of  wire  of  "  making  "  and 
"  breaking  "  the  current  in  an  adjacent  coil  of  wire. 

(4)  To  observe  the  change  of  effect  when  the  two  coils  have 
a  common  soft  iron  core. 

(5)  To  observe  whether  the  induced  current   aids  or  opposes 
the   movement. 

APPARATUS 

Weston  milli voltmeter,  with  zero  in  the  center  of  scale. 

2  coils  of  wire  50  to  100  turns  each  of  No.  28  D.  C.  C.  wire. 

2  dry  cells. 

Soft  iron  core. 

Connecting  wires. 

Procedure 

Connect  up  the  apparatus  as  shown  in  the  diagram,  leaving 
the  two  coils  apart.  See  Fig.  9. 

(a)  With  current  flowing  through  the  coil  A,  it  should  be 
moved  toward  the  coil  B  until  the  two  touch  and  have  their 


CURRENTS  INDUCED  BY  ELECTRO  MAGNETISM    27 

axes    coincident.      The    direction   of   movement   of   the    needle 
during  the  movement  of  the  coil  is  noted. 

(6)  After  allowing  the  needle  to  come  to  rest,  the  two  coils 
may  be  separated  and  the  direction  of  movement  of  the  needle 
during  motion  again  noted. 

(c)  By  placing  a  soft  iron  core  within  the  coil  A  and  repeat- 
ing the  movement  to  and  from  coil  B,  the  change  in  the  inten- 
sity of  the  thrust  of  the  needle  of  the  millivoltmeter  and  hence 
a  change  in  the  electro-motive  force  in  the  circuit,  is  observable. 

(d)  With  coils  A  and  B  side  by  side  (axes  coincident),  the 
current    through  coil  A  may  be  opened  and    closed  by  use  of 
one  of  the  wire  ends  at  the  battery.     The  direction,  as  well  as 


ZERO  CENTER 
MODEL  280 


FIG.  9. — CURRENT  INDUCED  BY  ELECTRO-MAGNETISM.     Turner's  Method. 

Instrument  Required  is  Model  280,  Weston  Zero  Center  Millivoltmeter. 
Range  100-0-100  Millivolts. 

the  intensity  of  the  thrust  of  the  needle  should  be  noted,  both 
on  closing  and  on  opening  the  circuit.  The  intensity  may  be 
still  further. varied  by  the  introduction  of  the  soft  iron  core  into 
the  coils. 

(e)  While  recalling  the  direction  of  thrust  of  the  needle  when 
current  was  made  to  enter  the  right-hand  binding  post  of  the 
millivoltmeter  from  the  simple  cell  of  the  previous  experiment, 
it  is  possible  to  trace  out,  by  Ampere's  hand  rule  for  rinding  the 
polarity  of  a  solenoid,  whether  the  magnetic  poles,  formed  by 
introduction  in  B,  assisted  or  hindered  the  movement  of  the 
magnetic  poles  in  A',  or  whether,  on  making  and  breaking  the 
circuit  in  (d)  the  polarity  of  B  and  A  was  such  as  to  hinder  making 
contact  and  prolong  the  contact  when  made,  or  the  reverse. 


28  EXPEEIMENTAL  ELECTRICAL  TESTING 

We  hoped  to  obtain  additional  exercises  on  induction  from 
other  sources,  showing,  for  instance,  the  inductive  effect  of  an 
electro-magnet  in  shunt  with  a  lamp  and  an  instrument;  so  that 
students  would  have  a  clear  conception  of  the  commercial  impor- 
tance of  induction  phenomena.  See  "  Practical  Physics,"  Black 
and  Davis,  page  312,  and  "  Elements  of  Electricity/'  Timbie, 
Chapter  10. — COMPILER'S  NOTE. 

THE  PHOTOMETER 

In  the  realm  of  practical  physics,  the  photometer  plays  a 
prominent  part  because  it  is  the  accepted  apparatus  for  deter- 
mining the  candle-power  or  luminosity  of  electric  lamps  or  other 
lighting  devices  as  expressed  in  terms  of  a  standard  lamp  or 
some  other  established  value  of  light.  Of  course  the  traditional 
standard  candle  is  obsolete,  and  the  amylacetate  standard  lamp 
has  also  been  relegated  to  oblivion;  both  giving  place  to  the 
incandescent  lamp  of  known  illuminating  power. 

In  view  of  the  fact  that  the  decrease  in  efficiency  of  an 
incandescent  lamp  is  large  when  carrying  an  underload,  and 
that  the  life  of  the  filament  is  shortened  enormously  by  an  over- 
load, stress  should  be  laid  upon  the  reason  for  marking  a  lamp 
•so  as  to  indicate  its  correct  e.m.f. 

It  gives  us  pleasure  to  find  that  many  high  schools  use  the 
photometer  in  their  physics  course,  and  that  we  are  therefore 
able  to  present  the  results  of  tests  made  by  high-school  students. 

EXPERIMENT  NO.  8 
AN  EXERCISE  IN  PHOTOMETRY 

Mr.  Lewis  H.  Fee,  Head  of  the  Science  Department  of  the 
Everett  High  School,  Everett,  Washington,  contributed  the 
following  excellent  exercise,  together  with  the  comments,  direc- 
tions and  conclusions  relating  thereto,  which  we  produce  ver- 
batim : 

"  The  following  laboratory  problem  is  one  of  a  list  of  those 
required  of  all  regular  physics  students  in  the  Everett  High 
School.  The  following  set  of  data  is  about  an  average  of  the 
results  as  a  whole.  No  originality  is  claimed  for  the  problem 
and  the  only  excuse  for  its  publication  is  to  offer  one  of  the 


AN  EXERCISE  IN  PHOTOMETRY 


29 


problems  which   show  the   correlation  between  the  laboratory 
work  in  light  and  electricity. 

"  Directions.  Set  up"  the  apparatus  as  in  the  accompanying 
sketch.  Have  your  set-up  checked  by  the  instructor  before 
closing  the  switch.  Move  the  screen  along  the  scale  until  the 
two  sides  are  equally  illuminated.  Read  the  distance  from 
the  unknown  lamp;  and  since  the  scale  is  100  cm.  long,  if  you 
subtract  this  reading  from  100  you  will  have  the  distance  from 
the  standard.  Make  three  or  four  determinations  of  this  dis- 
tance and  use  the  average  in  the  equation: 

c.p.  of  standard  :  c.p.  of  unknown  ::L2  :  I2, 
where    L  =  distance  from  screen  to  standard  lamp  and 
I  =  distance  from  screen  to  unknown  lamp. 


FIG.  10. — AN  EXERCISE  IN  PHOTOMETRY.     Fee's  Method. 
Instruments  Used  were  two  Model  156  Weston  Ammeters,  and  a  Model 
155  Weston  Voltmeter.     This  outfit  may  also  be  used  with  direct  current. 

"  This  equation  is  derived  from  the  well-known  law,  '  The  inten- 
sity of  illumination  varies  inversely  as  the  square  of  the  distance.' 
Since  the  intensity  is  the  same  at  the  screen,  the  intensity  or  c.p. 
of  the  source  must  vary  directly  as  the  square  of  the  distance. 

"  The  candle-power  is  measured  at  different  voltages  to 
show  that  there  is  a  relation  between  the  voltage  and  the  candle- 
power.  Lamps  of  different  kinds  and  ages  were  used  to  gain 
some  idea  of  economy  in  electric  lighting. 

"  Apparatus.  A  home-made  photometer.  (This  photom- 
eter is  merely  a  rectangular  box  16X16X116  cm.  with  doors  at 
either  end  for  the  insertion  of  the  lamps  and  also  one  near  the 
center  for  moving  the  screen.  See  Fig.  10. 


30 


EXPERIMENTAL  ELECTEICAL  TESTING 


"  The  screen  is  made  of  two  cakes  of  paraffin  separated  by 
a  piece  of  tinfoil  and  held  before  a  window  cut  in  a  rectangular 
metal  box  5X5X12  cm.  The  ends  of  this  metal  box  are  open 
towards  the  lamps  that  are  placed  in  either  end  of  the  large 
box.  It  is  100  cm.  from  center  to  center  of  the  lamp  sockets. 

'  Two  slide  resistances. 

"  Two  Weston  A.C.  ammeters*  Model  No.  156. 

"  One  Weston  A.C.  voltmeter,  Model  No.  155. 

"  One  standardized  incandescent  carbon  lamp  31.03  c.p.  at 
105  volts. 

RESULTS 
CARBON 


Volts 

105 

95                 85 

Amperes  
Distance  to  screen 

0.76 
50  9  cm 

0.72         !     0.65 
46  4  cm       41  4  cm 

Approximate  age  in  hours  of  use  
Rating  ... 

50.5  cm. 
50.5  cm. 
New 
100  watt 

46.4cm.      41.0  cm. 
46.0  cm.    '  41  .4  cm. 
New             New 
100  watt      100  watt 

Watts  per  c.p  
Per  cent  decrease  in  voltage 

32.69 

23.01            15.  58 
95              19 

IVr  cent  loss  in  c.p.  

29                 52 

CAIIBON 


Volts 

105 

95 

85 

Amperes  

0  90 

0  80 

0  70 

Distance  to  screen  

Approximate  age  in  hours  of  use  
Rating  .  .  . 

49.6  cm. 
49.5  cm. 
49-.  7  cm. 
1000 
32  c.p. 

45.5  cm. 
44.9  cm. 
45.9  cm. 
1000 
32  cp 

36.1  cm. 
36.0  cm. 
37.3  cm. 
1000 
32  c  i) 

Candle-power  
Watts  per  c  p 

30.05 
3  14 

21.51 
3  53 

10.55 
5  64 

Per  cent  decrease  in  voltage  
Per  cent  loss  in  c.p  

9.5 

28 

19.0 

65 

MAZDA 


Volts 

105 

95 

85 

Amperes  
Distance  to  screen  

0.35 
51.3  cm. 

0.35 
47.6  cm. 

0.35 
42.4  cm. 

Approximate  age  in  hours  of  use 

51.0  cm. 
50.5  cm. 
New 

47.2  cm. 
47.0  cm. 

New 

42.3  cm. 
43.0  cm. 
New 

Rating  
Candle-power 

40  watt 
33  43 

40  watt 
24  94 

40  watt 
17  05 

WTatts  per  c.p  
Per  cent  of  decrease  in  voltage 

1.10 

1.37 
9  5 

1.74 
19 

Per  cent  loss  in  c.p  

23 

49 

AN  EXERCISE  IN  PHOTOMETRY 


31 


MAZDA 


Volts  .  .  . 

105 

95 

85 

Amperes  .... 

0.40 

0.40 

0.40 

Distance  to  screen  

Approximate  age  in  hours  of  use  
Rating  
Candle-power 

51.4  cm. 
51.0  cm. 
51  .4  cm. 
500 
40  watt 
34  35 

47.0  cm. 
46.7  cm. 
46.5  cm. 
500 
40  watt 
23  88 

42.1  cm. 
41.0  cm. 
41.5  cm. 
500 
40  watt 
15  .  65 

Watts  per  c.p  
Per  cent  decrease  in  voltage 

1.22 

1.59 
9  5 

2.17 
19 

Per  cent  loss  in  c.p  

30 

54 

CONCLUSIONS 

"  In  order  to  arrive  at  any  definite  conclusions  it  would  be 
necessary  to  test  a  large  number  of  lamps,  hence  the  conclusions 
arrived  at  here  are  only  approximate. 

"  Incandescent  lamps  should  be  operated  at  nearly  their  rated 
voltage  as  the  c.p.  decreased  approximately  three  times  as  fast 
as  the  voltage.  It  is  also  more  economical,  as  is  shown  by  the 
'  watts  per  c.p.' 

"  That  the  metal  filament  is  the  more  economical  since  the 
'  watts  per  c.p.'  are  only  about  one-half  what  they  are  for  the 
carbon  filament. 

''  That  in  the  old  carbon  lamp  there  was  not  only  a  decrease 
in  c.p.,  but  also  an  increase  in  current  consumption,  making  it 
expensive  to  use. 

'  That  the  metal  filament  lamps  are  less  affected  by  age  and 
change  of  voltage  than  are  carbon  filament  lamps. 

"  (Signed)     WALTER  SUNDSTROM, 

"  GRANT  DURKEE." 

Quiz  for  Students.  Include  a  switch  in  the  main  line  so 
that  current  will  flow  through  a  metal  filament  and  a  carbon 
filament  lamp  simultaneously  when  the  circuit  is  closed.  Note 
that  the  light  from  one  lamp  "  arrives  "  at  the  screen  more 
quickly  than  from  the  other:  and  that  the  light  from  one  source 
also  disappears  sooner  when  circuit  is  broken.  Why? 

Does  the  light  from  one  lamp  travel  more  quickly  than  the 
other? — COMPILER'S  NOTE. 


32  EXPERIMENTAL  ELECTRICAL  TESTING 

EXPERIMENT   NO.  9 
PRACTICAL   INCANDESCENT  LAMP   TESTING 

(Prepared  by  tfee  Compiler.) 

The  following  experiments  have  a  direct  bearing  on  some 
of  the  problems  encountered  in  the  practical  construction  and 
testing  of  incandescent  lamps. 

They  also  serve  to  illustrate  that  a  thorough  mastery  of 
the  characteristics  of  Weston  instruments  is  no  insignificant 
accomplishment. 

Mount  a  lamp  socket  with  leads  on  a  board  having  dimen- 
sions of  about  3X6  inches. 

Screw  in  a  32-  or  else  a  16-c.p.  common  carbon  filament  110- 
volt  incandescent  lamp.* 

(1)  Connect  leads  with  a  Wheatstone  bridge  or  any  portable 
test  set,  and  measure  the  resistance  of  the  lamp  at  room  tem- 
perature.    Record  resistance  and  temperature. 

(2)  Substitute  a  60-  or  a  40-watt  metallic  filament  lamp  and 
repeat  the  test.     Record  results. 

Connect  the  leads  with  a  d.c.  service  line.f 

Include  in  the  circuit  the  carbon  lamp,  the  1.5  ampere 
range  of  a  Weston  Model  280  ammeter,  and  a  snap  or  knife 
switch.  Also  connect  a  voltmeter  of  suitable  range  across  the 
terminals  of  the  socket. 

(3)  Close  the  switch  and  let  the  current  flow  for  about  five 
minutes.     Then  break  and  instantly  remake  the  circuit,  keeping 
your  eye  on  the  pointer.     Note  that  it  will  overswing  slightly, 
before  becoming  steady.     Why? 

Notice  the  "  dead  beat "  action  of  the  pointer,  and  the 
rapidity  with  which  it  will  assume  its  true  position.  Record 
in  scale  divisions  the  extent  of  the  overswing.  Record  also  volt- 
age, and  current  consumed  when  pointer  is  steady. 

*  The  "  Gem  "  or  G.  E.  Metallized  Filament  lamp  will  not  serve  for  this 
experiment. 

t  NOTE. — Direct  current  is  necessary  for  these  tests;  but  if  only  A.C. 
service  is  available,  a  rectifier  may  be  used  to  good  advantage. 


PRACTICAL  INCANDESCENT  LAMP  TESTING  33 

(4)  Open  the  circuit  and  allow  the  lamp  to  cool  for  at  least 
5  minutes;  then  close  the  switch,  watch  the  pointer,  and  study 
its  action.     Observe  that  there  is  now  no  visible  overswing,  but 
on  the  contrary  a  noticeable  lag  in  its  movement  before  it  arrives 
at  its  position  of  maximum  deflection.     Why?     Repeat  test  (3) 
and  note  that  you  get  the  same  overswing  as  before. 

Then  open  the  switch,  wait  5  minutes  and  repeat  test  (4). 
Record  results. 

(5)  Substitute  a  60-  or  a  40-watt  metallic  filament  lamp  and 
repeat  tests  (3)  and  (4).     Record  all  results  obtained.     Describe 
the  action  of  the  pointer. 

(6)  Open  the  switch  and  insert  the  lamp  almost  up  to  its 
socket  in  a  glass  vessel  containing  water  and  cracked  ice  or 
snow.     (A  J-gallon  battery  jar  will  do  nicely.)     Unless  the  leads 
and  socket  are  waterproof,  see  that  they  remain  dry.     If  water 
accidentally  gets  into  the  socket,  unscrew  the  lamp  and  care- 
fully  dry   all   parts.     Measure    the    resistance    of   the  filament 
by  means  of  a  Wheatstone  bridge  or  any  other  test  set.     Record 
results,    giving   resistance,    and   temperature    of   solution.     The 
latter  should  be  near  0°  C.     Repeat  (6),  substituting  the  carbon 
filament  lamp.     Let  this    cool  for  at  least  40  minutes  belore 
recording  resistance  and  temperature. 

(7)  State    what    strike    you    as   the   most    significant    char- 
acteristic differences  between  these  filaments  as  revealed  by  the 
bridge  measurements,  (1),  (2)  and  (6). 

(8)  Apply   Ohm's   law.     Determine   the   respective   currents 
which  will  flow  through  the  filaments  at  room  temperature,  and 
at  the  temperature  of  melting  ice,  according  to  this  law,  when 
e  equals  voltage  at    the  socket  as  previously  recorded  in  tests 
(3)  and  (5),  and  r  equals  values  obtained  by  bridge  measurements. 
Compare  the  calculated  current  obtained  at  room  temperature 
with  the  ammeter  indications  in  the  preceding  tests  (3)  and  (5) ; 
when  current  was  steady;   and  if  there  are  any  differences  state 
why. 

(9)  In   any   test,    did   any   swing   of   the   ammeter   pointer 
indicate  a  current  which  was  equal  to  or  greater  than  the  cur- 
rent which  should  flow,   as  obtained  by  calculation  according 
to  Ohm's  law? 

(10)  Use  any  portable  current  indicator  obtainable,  in  place 
of  a  Weston  ammeter,  and  repeat  tests  (3)  and  (4)  with  it  if 


34  EXPERIMENTAL  ELECTRICAL  TESTING 

possible.     If  the  range  of  the  instrument  is  too  high  to  get  results 
with  one  lamp,  use  several  in  parallel.     Record  results. 

(11)  Explain  the  characteristics  of  the  Model  280  ammeter 
that  make  it  the  most  satisfactory  portable  instrument  for  these 
tests.    Base  your  statements  solely  upon  the  results  you  have 
obtained.     Do  not  generalize,  or  attempt  to  describe  the  instru- 
ment in  detail. 

(12)  Answer  the  quiz  question  under  photometer  experiment, 
and  explain  its  corelation  to  test  (4). 

ELECTROPLATING 

Department  of  Physics,  State  Normal  School, 

Bellingham,  Washington. 

Dec.  12,  1913. 
WESTON  ELECT.  INST.  Co., 

Newark,  New  Jersey. 

GENTLEMEN. — In  accordance  with  the  request  in  your  last 
communication,  I  am  mailing  you  a  student's  laboratory  report 
on  the  electro-deposition  of  copper.  Although  the  student  under 
stood  the  experiment  thoroughly  his  discussion  is  somewhat 
meager.  I  have  indicated  my  chief  criticisms.* 

I  do  not  believe  in  stereotyped  forms  of  reports.  I  like  to 
leave  as  much  as  possible  to  the  judgment  of  the  student,  call- 
ing for  additional  discussion  either  orally  or  in  writing,  if  not 
.enough  is  given. 

In  this  experiment  I  usually  find  the  current  obtained  from 
the  A.C.  mains  and  Nodon  valve  constant  enough  to  justify 
taking  a  number  of  amperage  readings  and  striking  an  average. 
In  the  second  test  of  this  report  the  current  varied  over  so 
great  a  range  f  (from  .85  amp.  to  1.1  amp.)  that  it  was  neces- 
sary to  note  the  length  of  time  that  it  stood  at  each  value  and 
to  compute  the  total  number  of  ampere-seconds  from  the  several 
amperages  and  the  corresponding  times. 

Very  respectfully, 

(Signed)  H.  C.  PHILIPPI. 

*  Mr.  Philippi  states:  "This  boy  has  had  only  one  year's  work  in 
Physics,  taken  when  a  sophomore  in  Normal  School.  Age  18  years." 

t  Variation  in  current  strength  was  probably  due  to  rise  in  temperature 
of  the  rectifier,  or  to  partly  exhausted  solution. 


ELECTROPLATING  WITH  COPPER 


35 


EXPERIMENT  NO.  10* 
ELECTROPLATING   WITH   COPPER 

"  In  electroplating  with  copper,  how  long  will  it  take  one 
ampere  of  current  to  deposit  one  gram  of  copper?  What  is 
the  electro-equivalent  of  copper? 

:t  The  alternating  current  of  the  city  lighting  system  is  changed 
to  a  direct  current  by  means  of  the  electrolytic  alternating  cur- 
rent rectifier.  See  Fig.  11. 


66666666 


D.C.AMMETER 


FIG.  11. — ELECTROPLATING  WITH  COPPER.    Philippi's  Method. 
Apparatus    Includes  an   Electrolitic  Rectifier   and  a   Model  280   Weston 

Ammeter. 

"  The  strength  of  the  current  is  regulated  by  being  run  through 
the  bank  of  incandescents. 

"  Difficulty  was  experienced  in  taking  the  second  set  of  read- 
ings because  of  the  inconstancy  of  the  current,  which  fluctuated 
between  0.85  amp.  and  1.1  amp. 

RESULTS 


Trial  (1) 

Trial  (2). 

"Wt  of  copper  deposited 

453  gm. 

.  568  gm. 

Time  of  deposit             

20  min. 

30  min. 

No  of  amperes 

1  15 

Time  1  amp  will  deposit  1  gm      

50.77 

51.36 

Electro  equivalent  

.  0003283  gm. 

.0003245  gm. 

*  This  experiment  is  of  special  importance  because  a  Nodon  valve  was 
used  in  connection  with  it.    See  page  000. — COMPILER'S  NOTE. 


36  EXPERIMENTAL  ELECTRICAL  TESTING 

"  No  satisfactory  average  could  be  found  for  the  amperage 
in  the  second  trial  owing  to  the  variation  in  the  current. 

>l  The  amount  of  any  metal  which  a  current  of  one  ampere 
will  deposit  in  one  second  is  called  the  electro-equivalent  of 
the  metal.  For  one  metal  this  amount  is  always  the  same.  Con- 
sequently this  is  a  very  accurate  way  to  measure  electricity. 
(Current  strength.) 

"  (signed)  L.  O.  GREENE." 
March  6, 1913. 

Instructors'  appended  comments: 

"  The  method  of  dealing  with  the  varying  current  should 
have  been  explained. 

"  In  which  direction  does  the  metal  in  a  plating  solution 
always  travel?  Upon  which  electrode  is  it  deposited?  " 


Copper  plating  is  of  great  commercial  importance  because 
iron  and  steel  are  always  plated  with  copper  before  giving  them  a 
finishing  coat  of  nickel. — COMPILER'S  NOTE. 


EXPERIMENT  NO.  11 

• 

THE  ELECTRO-CHEMICAL  EQUIVALENT  OF  A  METAL 

Substantially  the  same  experiment  as  the  foregoing  is  given 
herewith.  It  was  contributed  by  Mr.  Arthur  H.  Killen,  In- 
structor in  Physics,  Flushing  High  School,  Flushing,  New  York. 

This  experiment  was  performed  and  the  report  written  by 
one  of  the  senior  students.*  It  was  accompanied  by  a  very 
creditable  sketch  which  we  reproduce.  (See  Fig.  12.) 

Experiment.  To  find  the  electro-chemical  equivalent  of  a 
metal. 

Object.     To  find  the  electro-chemical  equivalent  of  copper. 

Apparatus.  Two  strips  of  copper,  a  copper  sulphate  solu- 
tion plating  bath,  a  Daniell  cell,  a  Weston  ammeter,  wire,  wire 
connectors. 

*  Mr.  Killen  informs  us  that  the  student's  age  was  18  years. 


THE  ELECTEO-CHEMICAL  EQUIVALENT  OF  A  METAL    37 

Work  Done.  I  carefully  weighed  a  strip  of  copper  which 
was  to  be  plated.  I  connected,  in  series,  the  Daniell  cell,  the 
Weston  ammeter  and  the  two  strips  of  copper  (the  one  care- 
fully weighed)  and  another  which  had  been  placed  in  the  copper 
sulphate  solution  electroplating  bath.  At  intervals  of  one  min- 
ute, I  took  readings  of  the  Weston  ammeter  during  forty  minutes 
and  averaged  them  to  find  the  amperage  or  current  strength 
during  the  forty  minutes.  I  then  removed  the  strip  on  which 


SULPHURIC 
ACID  SOLUTION 


COPPER  ON  WHICH  PLATE 
IS  TO  BE  DEPOSITED 


DANIELL  CELL 


COPPER  FROM  WHICH 
PLATE  IS  TO  BE  TAKEN 


COPPER  SULPHATE  SOLUTION 
ELECTRO  PLATING  BATH 


FIG.  12. — THE  ELECTROCHEMICAL  EQUIVALENT  OF  A  METAL  TEST.     (Repro- 
duced from  Student's  Sketch.)     Killen's  Method. 

Instrument  Used  was  a  Model  1,  Weston  Standard  Ammeter.     Range 
2  Amperes. 

the  copper  was  deposited  from  the  electroplating  bath  and  care- 
fully rinsed  and  dried  it.     I  then  reweighed  it. 


OBSERVATIONS  : 

Weight  of  strip  to  be  plated 22 . 952  grams 

Weight  of  strip  to  be  plated  after  forty  minutes.  23 . 532  grams 

Amount  deposited  in  forty  minutes 58     gram 

Average  amperage  or  current  strength 73    ampere 

Amount  deposited  by  .73  ampere  in  one  hour .        .  87    gram 
Amount  deposited  by  1  ampere  in  one  hour. ...     1 . 191  grams 
Amount  deposited  by  1  ampere  in  one  second. .        .0003308  gram 

Conclusions.  The  electro-chemical  equivalent  of  copper  is 
.0003308  gram,  that  is  .0003308  gram  of  copper  is  deposited 
by  one  ampere  in  one  second. 


38  EXPERIMENTAL  ELECTRICAL  TESTING 


MATHEMATICAL  WORK 

1st  weight  of  object  to  be  plated  ......   22  .  952  grams  by  .73  amp. 

Weight  of  object  to  be  plated  after 

forty  minutes  ..................   23  .  532  grams  by  .73  amp. 

Weight  of  deposit  at  end  of  40  minutes  .  .        .58   gram  by  .73  amp. 

.58 

^  =  .0145,  wt.  deposited  in  one  minute  by  .73  ampere. 

.0145X60  =  .87,  wt.  deposited  in  one  hour  by  .73  ampere. 

87 
:=^  =  1.191+wt.  deposited  by  one  ampere  in  one  hour. 

./  o 

1  191 

.00033083,  wt.  deposited  by  one  ampere  in  one  second. 


Sylvanus  Thompson  gives  .0003281  as  the  electro-chemical- 
equivalent  of  copper. 

(Signed)  HENRY  GREENBERG, 

(A.  H.  K.,  Instructor.) 


THE    USE    OF    THE    ELECTRIC    HEATER    IN    EFFICIENCY 

TESTS.* 

By  ERNEST  REVELEY  SMITH,  Syracuse  North  High  School. 

We  are  living  in  an  age  of  commercialism.  The  relation 
of  output  to  input  is  the  great  factor  which  determines  our 
investments  whether  large  or  small.  What  is  so  general  about 
us  cannot  fail  to  enter  our  laboratories.  The  toys  that  have 
been  used  so  long  as  equipment  are  rapidly  disappearing,  their 
purposes  well  served.  In  their  places  are  coming  the  newer 
commercial  appliances,  the  experimental  uses  of  which  commend 
themselves  instantly  to  the  boy  or  girl  as  something  worth  while. 

Among  the  commercial  offerings  to  the  Physics  laboratory, 
few  have  greater  possibilities  than  the  various  types  of  electric 
heaters.  The  very  fact  that  the  electric  stoves,  flatirons,  immer- 
sion heaters,  etc.,  are  taking  their  places  among  the  things  of 
our  every  day  life  makes  the  use  of  them  in  the  laboratory  both 
interesting  and  profitable. 

*  Reprinted  from  School  Science  and  Mathematics,  Vol.  13,  1913.  Avail- 
able through  the  courtesy  of  the  author. — COMPILER'S  NOTE. 


THE  ELECTRIC  HEATER  IN  EFFICIENCY  TESTS        39 


Also  they  are  the  most  adaptable  of  ^any  of  the  laboratory 
equipment  for  work  along  efficiency  lines,  since  all  that  is  neces- 
sary for  performing  the  experiment,  besides  the  heater  itself 
and  the  sources  of  current,  is  common  equipment  found  in  every 
laboratory.  Generally  we  use  an  electric  stove,  with  a  voltmeter 
and  an  ammeter  of  suitable  ranges,  a  flat  bottom  aluminum 
sauce  pan,  a  watch  and  a  thermometer. 

The  ammeter  is  connected  in  series  with  the  stove  and  the 
voltmeter  shunted  across  its  terminals,  see  Fig.  13.  (A  watt- 
meter may  be  used  in  place  of  these  instruments.)  While  the 
kettle,  and  the  kettle  with  the  water  are  being  weighed,  the  cur- 
rent is  turned  on  through  the  stove,  so  that  it  may  come  up  to 


VOLTMETER 


AMMETER 


TO  D.C.    LINE 


FIG.  13. — INSTRUMENTS  SHOWN  ARE  WESTON  MODEL  No.   1,  VOLTMETER 
AND  AMMETER.     Alternating  Current  Apparatus  may  be  Substituted. 

the  normal  working  temperature.  In  this  way  very  little  heat 
is  absorbed  by  the  stove  itself  during  the  actual  tests. 

The  temperature  of  the  known  weight  of  water  is  now  taken 
and  the  kettle  placed  on  the  stove  just  as  the  stop  watch  is 
started.  Voltmeter  and  ammeter  readings  are  taken  every  min- 
ute and  their  average  readings  used,  since  there  is  usually  con- 
siderable variation  in  the  potential  of  city  currents.  At  the  end 
of  a  given  time  (ten  minutes),  the  temperature  of  the  water  is 
read  after  stirring,  and  the  current  is  cut  off. 

From  the  average  current  and  fall  of  potential  through  the 
stove,  its  resistance  is  computed.  The  heat  developed  in  the 
stove  is  computed  from  the  well-known  formula,  calories  = 
0.24C2J^.  The  water  equivalent  of  the  kettle  is  found  from 


40  EXPERIMENTAL  ELECTRICAL  TESTING 

its  mass  and  specific  heat.  Then  the  heat  absorbed  is  the  mass 
of  the  water  including  the  water  equivalent  of  the  kettle,  multi- 
plied by  the  change  in  temperature.  The  efficiency  is  now 
obtained  by  dividing  the  calories  absorbed  by  the  calories  devel- 
oped. 

The  efficiency  tests  that  have  been  made  in  our  school  for  the 
past  three  years  have  given  results  varying  from  45  to  50  per 
cent  with  one  stove  and  from  65  to  70  per  cent  with  another. 

This  experiment  may  be  varied  in  several  details.  The 
apparent  efficiency  will  be  raised  from  10  per  cent  to  15  per  cent 
by  using  a  large  amount  of  water  in  place  of  400  or  500  grams. 
Covering  the  kettle  will  usually  raise  the  results  by  3  per  cent 
or  4  per  cent.  Again  enclosing  the  kettle  and  stove  in  an  asbestos 
jacket  will  give  a  result  some  5  per  cent  to  10  per  cent  higher. 
This  jacket  is  easily  made  from  asbestos  sheeting.  Another 
variation  brings  into  use  the  heat  of  vaporization.  The  experi- 
ment is  continued  until  part  of  the  water  has  boiled  away.  The 
kettle  and  contents  are  then  weighed.  The  heat  absorbed  is 

equal  to  the  sum  of  the  heat 
necessary  to  bring  all  the  water 
to  the  boiling  point  and  that 
required  to  vaporize  the  water 
lost  by  boiling.  This  method 
will  give  results  slightly  higher 
than  the  first. 

The  immersion  heater  (see 
Fig.  14)  gives  much  higher  re- 
sults than  the  stove.  Our  tests 
have  shown  an  efficiency  vary- 
ing from  90  per  cent  to  98  per 
cent.  The  heater  is  tested  in  the 
FIG.  14.— THE  IMMERSION  HEATER,  same  way  as  the  stove.  For 

general  use  about  a  laboratory 

this  device  is  very  satisfactory  as  it  will  heat  water  more  quickly 
than  gas  and  may  be  used  with  any  kind  of  a  dish. 

The  flatiron  makes  an  excellent  stove.  In  fact,  many  manu- 
facturers furnish  a  stand  to  hold  it  inverted  as  well  as  a  dish 
shaped  to  fit  its  working  surface.  Its  efficiency  is  not  as  high 
as  the  immersion  heater  or  stove,  ranging  from  40  per  cent  to 
60  percent,  depending  largely  upon  the  shape  of  the  kettle. 


THE  ELECTRIC  DISK  STOVE  OE  HOT  PLATE  41 

In  laboratories  having  electricity  but  no  stove,  an  incandescent 
bulb  may  be  used  for  efficiency  tests.  If  the  experiment  is  per- 
formed first  with  a  covered  opaque  calorimeter,  and  then  with 
a  glass  jar,  the  relative  amounts  of  energy  given  off  as  heat  and 
light  may  also  be  determined. 

In  any  of  the  above  experiments  the  cost  of  electricity  may 
be  easily  computed.  If  the  pupil  has  found,  earlier  in  his  work, 
the  cost  of  using  a  gas  stove  or  burner  for  a  similar  length  of 
time,  he  now  has  data  for  an  interesting  comparison. 

Usually  I  divide  the  class  into  several  squads  of  five  or  six 
for  these  experiments.  While  one  squad  is  performing  this  experi- 
ment, the  other  members  of  the  class  are  working  on  an 
experiment  for  which  we  have  individual  apparatus.  One 
pupil  from  each  squad  weighs  the  kettle  and  water,  another 
reads  the  thermometer,  another  has  charge  of  the  wiring,  while 
others  read  the  voltmeter  and  ammeter  or  hold  the  watch.  This 
insures  the  constant  attention  of  each  member  of  the  squad 
since  he  has  something  to  do  which  is  definite  and  vitally  important 
to  the  experiment.  Of  course,  the  entire  experiment  may  be 
performed  by  two  pupils,  if  desirable,  or  made  a  class  exercise, 
letting  several  pupils  make  the  readings  for  the  class.  Which- 
ever way  it  is  done,  it  furnishes  one  of  the  most  instructive  as 
well  as  popular  experiments  in  our  laboratory. 


EXPERIMENT  No.    12 
THE   ELECTRIC   DISK   STOVE    OR  HOT  PLATE  * 

Contributed  by  Mr.  H.  C.  PHILIPPI,  Head  of  Science   Department,  State 
Normal  School,   Bellingham,  Washington. 

Object.  To  determine  the  efficiency  of  an  electric  disk  stove 
or  hot  plate. 

Apparatus.  Electric  disk  stove;  Weston  voltmeter;  Weston 
ammeter;  two-quart  copper  tea-kettle;  thermometer;  balance 
and  weights;  watch.  See  Fig.  15. 

*  Contributor  states:  "The  results  are  those  actually  obtained  by 
members  of  my  class." — COMPILER'S  NOTE. 


42 


EXPERIMENTAL  ELECTRICAL  TESTING 


For  convenience  in  making  connections  the  plug  and  flexible 
cord  are  removed  from  the  stove,  the  stove  mounted  upon  a 
board  and  its  terminals  permanently  attached  to  binding  posts 
in  the  board.  The  connections  are,  of  course,  those  of  any 
electrical  power  test.  Before  making  the  test  which  is  to 


A. C. LINE 

FIG.  15. — EFFICIENCY  TEST  OF  AN  ELECTRIC  DISK  STOVE  OR  HOT  PLATE. 
(Reproduced  from  Students'  Sketch.)     Philippi's  Method. 

Instruments  used  were  Model  155  Weston  A.  C.  Ammeter,  range  10 
amperes,  and  Model  155  Weston  A.  C.  Voltmeter,  range  150  volts. 
These  instruments  may  also  be  used  with  direct  current. 


become  a  matter  of  record,  it  is  well  to  make  a  preliminary  test 
to  get  the  stove  into  a  steady  thermal  state.  With  the  two- 
quart  kettle,  it  will  be  found  convenient  to  use  about  four 
pounds  of  water  and  allow  current  from  110-volt  lighting  mains 
to  pass  for  about  ten  minutes.  If  the  current  runs  much  above 
five  or  six  amperes,  the  time  must  be  shortened. 


COST  OF  OPERATING  AN  ELECTRIC  FLAT  IRON       43 
RESULTS  OBTAINED  BY  STUDENTS 


Trial  (1). 

Trial  (2). 

Trial  (3). 

Weight  of  water  used  

4.4  lb. 

4.41b. 

4.41b. 

Weight  of  tea-kettle 

1  0  lb 

1  Olb. 

l.Olb. 

Water  equivalent  of  tea-kettle 
aDDr 

0  1  lb. 

0  1  lb. 

0.1  lb. 

Initial  temperature  Fahrenheit 
Final  temperature  

66.2° 
129.2° 

59.0° 
123.8° 

59.9° 
123.8° 

Rise  in  temperature.  ,.  
Average  voltage  applied  
Average  current  in  amp 

63.0° 
107.0 
4  95 

63.8° 
107.0 
4  95 

62.9° 
107.0 
4.95 

Time  current  ran.                    .  . 

10  min. 

10  min. 

10  min. 

Heat  gained  (B.T.U.)  
Power  input  (watts)  

283.5 
530 

287.1 
530 

283.0 
530 

Energy   input    (watt-sec.) 
(Joules)  
Heat  equivalent  of  this  energy 
1055  watt-sec.  =  1  B.T.U...  . 
Efficiency  of  stove  and  kettle  . 
Average  efficiency  
Cost  per  hr.  to  operate  this 
stove  at  lOc.  per  kw.  hr  

318,000 

301.  4  B.T.U. 
94.0% 

94.4% 

5.3c. 

318,000 

95.2% 

318,000 
93.9% 

EXPERIMENT  No.  13 

COST  OF  OPERATING  AND  EFFICIENCY  OF  AN  ELECTRIC 

FLAT   IRON 

Contributed  by  Mr.  F.  H.  BEALS,  Barringer  High  School,  Newark,  N.J. 

Object.  To  determine  (1)  Cost  of  ironing  roller  towels.  (2) 
Efficiency  of  an  electric  flatiron. 

Apparatus.  Electric  flatiron  weighing  5.8  pounds  rated  as 
weighing  6  pounds  and  using  110  volts  and  4.2  amperes,  ironing 
board  38"X14J",  having  no  padding  but  covered  with  a  roller 
towel  stretched  over  the  surface,  dampened  towels,  Weston 
wattmeter  (150  volts  and  5  amperes),  fuse  blocks  and  connections, 
balance,  scales  and  weights.  See  Figs.  16  and  17. 

Performed  by  ELIZABETH  ARCULARIUS.  Assisted  by  RUTH 
A.  HUSK  and  KATHARINE  VAN  ALEN. 

MANIPULATION 

Directions.  Sprinkle  towels  in  preparation  for  ironing.  Con- 
nect up  iron  and  wattmeter  as  shown  in  diagram,  Fig.  17.  Let 
the  current  run  2J  minutes  to  heat  the  iron.  Iron  rapidly  so 


44 


EXPERIMENTAL  ELECTRICAL  TESTING 


as  to  waste  as  little  heat  as  possible.  To  find  the  number  of 
calories  required  to  evaporate  water,  allow  80  calories  per  gram 
to  heat  from  room  temperature  to  temperature  of  evaporation, 
and  536  calories  to  evaporate  water.  Let  A  represent  output 
in  calories  =  loss  of  weight  X  (536 +80).  To  find  heating  power 
of  current,  let  B  represent  input  in  calories  =  watts X sec. X. 24. 
To  find  efficiency  use  A  +  B.  *To  find  cost  allow  10  cents  per 
K.W.  hr.  Cost  =  watts -f- 1000 Xhr.XlOc. 


FIG.  17. — BEALS'  WATTMETER  METHOD.     (Reproduced     from     Connection 

Chart.) 

Instrument  used  was  a  Model  16  Weston  Wattmeter  No.  2- A.  Ranges 
5  Amperes  and  75  and  150  volts. 

Method.  General  Principle:  After  the  towels  were  damp- 
ened and  weighed,  the  ironing  was  commenced.  The  wattmeter 
was  read  at  regular  intervals  and  recorded.  When  the  towels 
were  ironed  they  were  weighed  again.  The  length  of  time  taken 
for  ironing  was  also  noted.  The  average  number  of  watts  was 
found,  and  the  loss  of  weight  in  grams  due  to  evaporation  was 
determined.  Throughout  the  experiments  readings  were  taken 
as  recorded  below. 

CASE  I.  A  wet  towel  was  used.  In  finding  the  efficiency 
no  allowance  was  made  for  evaporation  or  absorption. 


COST  OF  OPERATING  AN  ELECTRIC  FLAT  IRON       45 


CASE  II.     Conditions  the  same  as  in  Case  I. 

CASE  III.  Five  towels  were  dampened  the  evening  before 
as  for  ordinary  ironing.  In  finding  the  efficiency  no  allowance 
was  made  for  evaporation  or  absorption. 

CASE  IV.  A  very  damp  towel  was  used.  In  finding  the 
efficiency  allowances  were  made:  (1)  For  evaporation,  due  to 
the  heat  of  the  room,  that  would  have  taken  place  in  the  8J 
minutes  without  ironing.  (2)  For  absorption  of  moisture  by 
towel  covering  board.  (3)  For  evaporation  (while  airing  4 
minutes)  due  to  heat  of  towel,  above  room  temperature. 

No  allowance  was  made  for  heating  the  iron.  The  temper- 
ature of  the  room  was  22°  C.  It  may  be  of  interest  to  know 
that  the  relative  humidity  for  the  day  was  55  per  cent,  but  this 
was  not  used. 

DATA  AND  CALCULATIONS 
No  allowances  for  correction 


Case. 

I 

II 

ill 

Condition  of  towel  
Weight  wet.  .        

1  wet 
413  0  g. 

1  very  wet 
421  2  g. 

5  slightly  wet 
1255  4  g. 

Weight  ironed  

273  .  5  g. 

268  3  g. 

1180.6  g. 

Loss  of  weight 

139  5  g 

152  9  g 

74  8  g. 

Watts  average  

531  5 

541  3 

535  0 

Time  taken  for  ironing  .... 
Efficiency 

13.5  min. 
80  1% 

15.0  min. 
80  6% 

8.5  min. 
70% 

Cost  of  ironing  towels  

$.012 

$.013 

$0.007 

Allowance  for  corrections 

Case.  IV 

Condition  of  towel 1  very  damp 

Time  to  heat  iron 1.5  min. 

Watts — average : . .  531 . 0 

Weight  wet 382 .9  g. 

Weight  ironed 234 . 4  g. 

Loss  of  weight  by  ironing 148 . 5  g. 

Time  actually  consumed  in  ironing 10.0  min. 

Weight  of  towel  covering  board  (before  ironing) 233 . 9  g. 

Weight  of  towel  covering  board  (after  ironing) 247 . 6  g. 

Increase  in  weight  of  towel  covering  board 13 . 7  g. 

Weight  of  towel  immediately  after  ironing 234 . 4  g. 

Weight  of  towel  dampened  to  same  degree  as  one  ironed 382 .9  g. 

Weight  of  same  towel  hanging  8|  min.  in  ah* 366.6  g. 

Loss  of  weight  in  this  second  towel 15 . 3  g. 

Efficiency 88.5% 

Cost  of  ironing  one  very  damp  towel t     $0 . 007 


46  EXPERIMENTAL  ELECTRICAL  TESTING 

Efficiency.     Case  I. 

139.5  X  (536 +80)         85932 
531 X  13.5  X60X.24     103226.4     M^/0' 


Case  II. 


152.9  X  (536 +80)  *     94186.4 
541.3X15X60X.24     116920.8     5U'D/0' 


Case  III. 


74.8  X  (536+80)       46076.8  ^ 

535X8.5X60X.24      65484  /0* 


Case  IV. 


(148.5 -13.7- 15.3)  (536+78)  =73373 

531 X 10  X  60  X. 24  76464    yb'u/0< 


Conclusion.  It  seems  to  me  that  the  reason  why  the  efficiency 
is  lower  in  Case  III  is  because  the  amount  of  moisture  to  be 
evaporated  is  not  so  great  in  this  case  as  in  the  others.  Cer- 
tainly the  cost  of  ironing  depends  upon  the  quantity  of  water 
used  in  sprinkling. 

The  cost  of  ironing  five  towels  moistened  as  in  ordinary 
ironing  was  found  to  be  0.7  cent. 

Computations  were  checked  by  George  Y.  Sosnow. 


EXPERIMENT  NO.  14 
BOILING  AN  EGG  BY  MEANS   OF  ELECTRICITY 

Contributed  by  Mr.  ERNEST  R.  SMITH,  Vice-Principal  of  the  Syracuse  North 
High  School,  Syracuse,  N.  Y. 

Object.  To  find  the  cost  of  boiling  an  egg  by  means  of 
electricity,  and  incidentally  to  determine  the  efficiency  of  the 
stove. 

Apparatus.  Small  disc  stove,  Model  155  Weston  Voltmeter; 
Model  155  Weston  ammeter;  aluminum  kettle;  thermometer; 


BOILING  AN  EGG  BY  MEANS  OF  ELECTRICITY        47 

platform  balance  and  weights;   eggs;   watch  and  source  of  A.G. 
current. 


HUBBEL  PLUG 


10  AMP.  FUSE 


FIG.  18. — BEALS'    A.    C.    VOLTMETER   AND    AMMETER    METHOD.     (Repro- 
duced from  Connection  Chart.) 

Instruments  used  were   Model   156  Weston  A.  C.  Voltmeter,   range  150 
Volts  and  Model  156  Weston  Ammeter,  range  10  amperes. 


Results. 

Weight  of  kettle 

Weight  of  kettle  and  cold  water 

Temperature  of  cold  water 

Weight  of  kettle   and    contents  after  boiling 

egg  for  (3)  min 

Temperature  of  boiling  water  for  day 

Temperature  change  of  water 

Fall  of  potential  through  stove 

Current  through  stove 

Resistance  of  stove  ( R =-^  j 

Heat  developed  in  stove  in  20  minutes  =  .24 

C2#*  =  .24X(5.31)2X21.09X20X60 

Water  equivalent  of  kettle  (MXS) 


215.4  grams 
1222. 6  grams 
23.8°  C. 

1151  grams 
99.45°C. 
75.65°C. 
112  volts 

5.31  amps. 

21.09  ohms 

171,336  cal. 
47 . 4  grams 


48  EXPERIMENTAL  ELECTRICAL  TESTING 

Heat  absorbed  by  water  in  coming  to  the  boil- 

ing point,  1054.6X75.65  ................  79,780.5  cal. 

Heat  used  in  boiling  away  71.6  grams  of  water 

71.6X537  ............................  38,449.2  cal. 

Total  heat  absorbed  by  water  ..............    118229.7  cal. 

,    .  Output     118229.7 

Efficiency  of  stove  =    —   =      +.  .  .  . 


112X5  31 
Kilowatt-hours  of  work  -     y^  —  Xf  .......  .198  kwt.  hr. 

luuu 

Cost  of  operating  stove  to  boil  egg  for  3  min- 

utes at  8j£  per  kwt.hr  ..................  1.6  cts.* 

(Signed)  DELPHINE  BE  QUILLARD. 
Dec.  8,  1913. 

Manipulations.  The  small  electric  stove  was  connected 
to  the  A.C.  main  and  an  ammeter  put  in  series  with  it  and  a 
voltmeter  shunted  across  its  terminals.  I  found  the  weight  of 
the  kettle  empty,  and  filled  two-thirds  full  of  cold  water.  After 
taking  the  temperature  of  the  water,  the  kettle  was  placed  on 
the  stove  and  the  current  turned  on.  Readings  of  the  volt- 
meter and  of  the  ammeter  were  taken  every  minute.  When 
the  water  began  to  boil  the  egg  was  put  in  and  the  boiling  con- 
tinued for  three  minutes. 

The  kettle  and  hot  water  were  weighed  again.  From  the 
barometer  reading,  the  temperature  of  boiling  water  for  the 
day  was  determined.  The  computations  as  indicated  in  the 
tabulation  were  made.  The  cost  of  boiling  the  egg  was  found 
to  be  1.6  cents  and  the  efficiency  of  the  stove  69  per  cent. 

*  Several  eggs  might  have  been  cooked  at  a  very  slight  increase  over 
the  above  cost  for  one,  as  the  dish  and  quantity  of  water  were  sufficiently 
large.  —  INSTRUCTOR'S  NOTE. 


THE  IMMERSION  HEATER  49 

EXPERIMENT  NO.  15 
THE   IMMERSION   HEATER 

The  experiment  was  repeated,  using  a  smaller  dish  and  an 
immersion  heater.  See  Fig.  14. 

Results : 

Weight  of  dish 145 . 2  grams 

Weight  of  dish  and  cold  water 455 . 0  grams 

Temperature  of  cold  water 23 . 8°  C. 

Weight  of  kettle  and  contents  after  boiling  egg 

3  minutes  (4.5  minutes) 425 . 0  grams 

Temperature  of  boiling  water  for  day 99.45°  C. 

Temperature  change  of  water 75.65°  C. 

Fall  of  potential  through  heater 111.0  volts 

Current  through  heater 6 . 06  amps. 

Resistance  of  heater 18.31  ohms 

Heat  developed  in  4J  minutes  = 

.24  X(6.06)2X  18.31X4.5X60 43,505.  leal. 

Heat  absorbed  by  water  in  coming  to  boiling  pt.  24,533 . 3  cal. 

Heat  used  in  boiling  away  30  gms.  of  water. .  .  16,110.0  cal. 

Total  heat  absorbed 40,643 . 3  cal. 

Efficiency  of  heater 93 . 4% 

111X6.06,  4.5 

Work  done  by  heater  -  ., -„- — X-^: .05  kwt.  hr. 

10UU  bU 

Cost  of  boiling  egg  at  8ff  per  kwt.  hr 0.4  ct. 

(Signed)  DELPHINE  BE  QUILLARD. 
December  8,  1913. 

See  Fig.  15  (Philippics  arrangement)  for  suitable  diagram  of 
connections  containing  instruments  used. — COMPILER'S  NOTE. 

EXPERIMENT  NO.  16 

MAKING   COCOA  AND   CANDY   WITH   THE   AID    OF 
ELECTRICITY 

Contributed  by  F.  H.  REALS 

Object.  To  find  the  cost  of  making  Cocoa  and  Candy 
(Fondant)  and  of  boiling  water  on  the  electrical  disk  stove;  also 
determining  the  efficiency  of  the  stove. 


50 


EXPERIMENTAL  ELECTRICAL  TESTING 


Apparatus.     Weston   Voltmeter   and   Ammeter,    Disk   Stove, 
Double  Boiler,  Thermometer,  Graduate.     See  Fig.   18. 
Performed  by  Helen  Burnett  and  Marion  Butler. 


Making  Cocoa, 
Experiment  A. 

Making  Fondant  Candy, 
Experiment  B. 

Boiling  Water, 
Experiment  C. 

Case  I 

Case  I 

Ingredients 

IngVedients 

Cocoa,     8    level    tea- 
spoonfuls. 
Sugar,    6    level    tea- 

Sugar,    1    cup    (2    oz.) 
J  Water,  f  cup,  (96  c.c.) 
Cream    of    tartar,    ^ 

1000  c.c.  of  water  in 
the  lower  part  of  the 
double  boiler,  and  upon 

spoonfuls. 
Cold    water,    2    cups 

teaspoonful. 

the  disk-stove. 
Bring  to  boiling  point, 

(500  c.c.). 

Method 

recording  time  taken 

Cold     milk,     2    cups 

Mix    sugar,    cream    of 

to  perform  experiment. 

(500  c.c.). 

tartar,    and    water     to- 

Method 
Pour    the  ^  cold    milk 
and     water     into     the 
metal  boiler  on  the  disk- 
stove.     Make  the  elec- 
trical    connections     as 
shown   on   the  sketch; 
record   time   and   turn 
on  current. 
Mix    the    cocoa    and 
sugar  well  together  in 
a  bowl;    add  £  cup  of 
cold  water  and  stir  to 
make  a  thin  paste. 
Pour  some  of  the  hot 

gether  in  lower  part  of 
double  boiler.     Place  on 
the     disc-stove,     having 
had    the    current    on    2 
min.  to  allow  for  heat- 
ing.    Record  time. 
Stir  mixture  until  sugar 
is  completely  dissolved, 
boil    uncovered    until   a 
drop     of     the     mixture 
dropped    from    the    end 
of  a  spoon  spins  a  thread, 
or  until  it  forms  a  thick, 
jelly-like         consistency 
when  dropped  into  cold 

TTTQf  Of 

Case  II 

Place  250  c.c.  of  water 
in  the  lower  part  of  the 
double  boiler,  and  500 
c.c.  of  water  in  the 
upper  part.  Place  both 
parts  on  the  disk-stove, 
together  and  heat. 
Record  time  taken  to 
heat  water  in  upper 
boiler  and  obtain  other 
necessary  data. 

mixture  into  the  bowl 
and  wash  out  all   the 
cocoa   into   the   boiler. 
Bring    to    a    boil    and 
boil  three  min. 

WdtCl  • 

Turn  off  current,  first 
recording     time.      Pour 
the     mixture     upon     a 
iwell-greased  marble  slab 
or  a  flat  platter.     When 

f~^QCO    TT 

sufficiently  cool  so  that 

V^d/bC    1J. 

the    mixture    does    not 

Ingredients 

adhere     to    the     finger 

Cocoa,  3  level  table- 

when   touched    in    the 

spoons. 

center,  beat  with  wooden 

Sugar,  3  level  table- 

spoon   until     the    mix- 

spoons. 

ture  becomes   too   hard 

Water,    2    cups    (500 

to    beat,     then     knead 

c.c). 

with   the   hands.     When 

Milk,  2  cups,  (500  c.c.) 

it    becomes    sufficiently 

M  +V> 

cooled,    roll    into    small 

ivietnoa 

balls  for  bonbons. 

Mix  cocoa,  sugar,  and 

water  thoroughly. 

Bring  milk  to  boiling 

point;     add    first   mix- 

ture  and   bring   all   to 

scalding  point.    (About 

80°  C.) 

MAKING  COCOA  AND  CANDY 


51 


Outer  Parts  of'  Double  Boiler. 

Both 
Parts  of 
B.  B. 

Cocoa, 
Experiment  A. 

Candy, 
Experi- 
ment B. 

Water, 
Experiment  C. 

Time  required  to  heat  plate  
Volts  (average)  

2  min. 
Case  I 
114.5 
3.6 
412.2 
630       g. 
0.1 
63.0  g. 
(2c.)500c.c. 
(2c.)500c.c. 

2  min. 
Case  II 
119.0 
3.8 
452.2 
630       g. 
0.1 
63.  Og. 
(2c.)  500  c.c. 
(2c.)500c.c. 
100°  C., 

79°  C. 
25°  C. 
15°  C. 
14.5  min. 
$.0109 

2  min. 

2  min. 
Case  I 
117 
3.7 
432.9 
630      g. 
0.1 
63.  Og. 
1000  c.c. 

96°  C. 
25°  C. 

15  min. 
$.0108 

2  min. 
Case  II 
117 
3.7 
432.9 
630      g. 
0.1 
63.0  g. 
750  c.c. 

95°  C. 
25°  C. 

32  min. 

$0  .  023 
26% 

29% 

115 
3.7 
425  .  5 
630      g. 
0.1 
63.  Og. 
96  c.c. 

2i'°'c! 

15.5  min 
$.0116 

Amperes  (average)                         

Watts-volts  amperes  

Weight  of  boiler  
Water  equivalent  of  boiler  (approx.) 
Water  equivalent  of  boiler  (approx.) 
Quantity  of  water  used 

Quantity  of  milk  used  
Tern,  of  water  alone  after  8  min.  .  .  . 

Tem.      (cocoa     and     water)      when 
finished  
Tem   water  before  heating 

92°  C. 
26°  C. 
15.5°  C. 

24  min. 
$.016 

Tem.  milk  before  heating  

Total  time  taken  to  make  
Cost  to  make  100  )  c.c.  of  cocoa.  .  .  . 
Cost  to  make  235  g.  of  candv  
Cost   to    boil   1000  c.c.    of  water  in 

Cost   to   heat   250    c.c.    of   water  in 
the  lower  boiler,  and  500   c.c.    of 
water  in  the  upper  boiler,  i.e.,  cost 
of  both 

Practical  efficiency  (water)  
Theoretical    efficiency     (water     and 
dish)  



72% 
81% 



76% 
81% 

Conclusion.  It  is  evident  that  the  electric  disk  stove  is  not 
nearly  as  efficient  when  both  parts  of  the  doubler  boiler  are  used 
as  when  the  single  dish  is  used.  And  also  that  the  real  efficiency 
calculated  for  actual  heating  of  water  is  less  than  efficiency 
reckoned  on  the  basis  of  amount  of  metal  and  water  used. 


Practical  efficiency  = 


Weight  of  water  X  change  in  temp. 
No.  watts X No.  seconds X. 24 


Theoretical  efficiency  = 

(weight  of  water +.1  wt.  of  boiler)  change  in  tem. 
No.  wattsXNo.  seconds X. 24 

In  calculating  efficiency  we  considered  two  cases. 

(1)  Practical  efficiency,  when  we  took  into  consideration  only 
the  heating  of  the  water  actually  used  and  (2)  theoretical  effi- 
ciency, when  we  considered  the  heat  absorbed  by  both  the  water 
and  the  dish. 


52  EXPERIMENTAL  ELECTRICAL  TESTING 

The  cost  of  making  2  quarts  of  cocoa  was  about  2.7  cents; 
for  making  over  J  pound  of  candy,  1.16  cents. 

INSTRUCTOR'S  NOTE.  The  second  year  of  science  for  girls 
at  Barringer  High  School  differs  from  the  course  for  boys,  one- 
fifth  of  the  girls'  year  being  devoted  to  cooking.  The  work  in 
electricity  for  girls  is  correlated  with  this  branch  of  domestic 
science.  All  the  electrical  experiments,  except  Case  II  above, 
were  performed  in  the  physical  laboratory;  the  second  method 
of  making  cocoa  seemed  to  the  Cooking  Department  more 
satisfactory. 

There  can  be  no  doubt  that  the  exercises  in  electrical  heating 
and  cooking  have  touched  the  daily  life  and  experience  of  the 
girls  who  have  done  them.  They  are  incomparably  superior 
to  the  old,  conventional  experiments  of  the  physical  laboratory, 
so  far  as  the  girls  are  concerned. 

It  may  be  of  interest  to  observe  that  the  above  method  of 
measuring  efficiency  by  the  amount  of  water  evaporated  has 
been  used  at  the  Barringer  High  School  to  obtain  the  efficiencies 
of  an  electric  toaster  and  an  electric  stove,  and  conversely  to 
obtain  the  latent  heat  of  vaporization. 

The  highest  efficiencies  were  obtained  when  there  was  con- 
tact, as  in  the  case  of  the  electric  flat  iron,  and  the  lowest  when 
the  heating  was  chiefly  by  radiation,  as  in  the  electric  toaster. 

Domestic  electrical  contrivances  are  not  of  course  primarily 
designed  to  serve  as  a  means  of  affording  physical  quantities 
which  may  be  readily  determined  with  scientific  exactness; 
but  rather  to  permit  useful  work  to  be  performed  with  expedi- 
tion, convenience  and  minimum  cost. 

Hence  individual  results  obtained  from  different  sources 
may  disagree,  without,  however,  detracting  from  their  educational 
value. 


Lack  of  space  compelled  us  to  defer  the  publication  of  several 
additional  exercises  on  domestic  electrical  apparatus.  Upon 
request  we  will  mail  copies  of  the  following : 

Cost  of  Frying  on  the  Disk  and  Oblong  Stoves. 

Cost  of  Operating  an  Electric  Toaster. — COMPILER'S  NOTE. 


AN  ELECTROLYTIC  CURRENT  RECTIFIER  .  53 

AN   ELECTROLYTIC    CURRENT   RECTIFIER 

(Prepared  by  the  Compiler) 

In  the  following  pages  we  devote  considerable  space  to  a 
description  of  an  apparatus  known  as  a  Nodon  Valve  or  Electro- 
lytic Current  Rectifier. 

We  were  extremely  surprised  at  being  unable  to  find  a  single 
High  School  text-book  which  gave  even  a  cursory  reference  to 
this  subject;  and  although  we  do  not  manufacture  apparatus 
of  this  type,  we  are  publishing  the  results  of  our  experiments. 

We  do  so  because  there  are  many  schools  which  are  limited 
to  alternating  current  line  service,  the  character  of  which  nec- 
essarily is  not  adapted  to  the  performance  of  many  experiments 
requiring  direct  current,  which  should  form  part  of  a  High 
School  course. 

In  addition  apart  from  its  practical  value  as  a  means  of 
transforming  alternating  current  into  pulsating  direct  current, 
the  apparatus  merits  the  careful  consideration  of  all  science 
teachers  because  it  may  be  easily  and  cheaply  constructed; 
and  forms  the  basis  of  an  experiment  that  should  be  included 
in  every  laboratory  schedule. 

That  there  is  a  pressing  demand  for  some  such  device  is 
testified  to  by  the  numerous  inquiries  we  have  received  for 
information  pertaining  to  a  simple  form  of  rectifier;  and  it  is  a 
great  pleasure  to  present  the  results  of  our  investigations. 

While  our  work  is  not  exhaustive,  it  furnishes  ample  material 
for  exercises,  and  when  practicable  we  should  be  glad  to  receive 
reports  from  instructors  wrho  decide  to  include  the  rectifier  as 
part  of  their  laboratory  equipment. 

Students  are  certain  to  become  interested  in  a  method  of 
converting  "  a.c."  into  "  d.c.,"  and  especially  will  this  be  the 
case  when  it  is  explained  how  often  some  type  of  converter  is 
used  in  practical  work,  when  it  becomes  necessary  for  instance, 
to  charge  an  automobile  storage  battery  at  once,  and  no  "  d.c." 
is  available. 

The  Nodon  valve  form  of  rectifier  has  been  selected  for 
description,  because  it  is  extremely  simple  in  construction,  and  a 
"  valve  "  can  be  made  in  a  few  minutes  at  a  trifling  cost. 


54  EXPERIMENTAL  ELECTRICAL  TESTING 

It  cannot  be  ranked  as  an  efficient  form  of  rectifier,  and 
no  such  claim  is  made  for  it;  but  fortunately  great  efficiency  in 
transformation  is  not  a  matter  of  vital  importance  in  school 
laboratories,  the  main  desideratum  being  to  obtain  direct  cur- 
rent service  when  required. 

Although  also  somewhat  erratic  in  its  behavior,  in  that  the 
pulsating  direct  current  it  furnishes  is  not  always  steady,  it 
would  be  difficult  to  find  a  single  piece  of  apparatus  which  is 
more  interesting  and  instructive  than  a  Nodon  Valve,  when 
used  in  connection  with  accurate  measuring  instruments. 

THE  NODON  VALVE 

Small  Nodon  Valves  are  inexpensive  and  are  very  easily 
made.  All  that  is  required  is  a  jar  containing  a  plate  or  rod  of 
aluminum  partly  immersed  in  a  saturated  solution  of  bicarbonate 
of  soda,  and  an  inactive  conductor. 

Sheet  aluminum  yg-  inch  thick  costs  less  than  $1.00  per 
square  foot  at  retail.  If  it  is  too  tough  or  brittle  to  bend  easily, 
aluminum  can  be  softened  by  holding  over  a  Bunsen  flame.  In 
order  to  obtain  good  results  it  is  of  great  importance  that  the 
aluminum  employed  is  practically  pure.  Much  of  the  commer- 
cial aluminum  used  in  manufacturing  condensers,  etc.,  is  adul- 
terated with  zinc. 

We  found  that  such  material  gave  low  efficiency,  in  some 
cases  even  causing  the  pointer  of  the  direct-current  instrument 
to  vibrate  to  an  extent  likely  to  damage  the  movement. 

For  experimental  purposes,  several  of  these  valves  were  con- 
structed at  the  Weston  laboratories.  They  consisted  of  glass 
jars  6  inches  in  diameter  and  7  inches  in  height,  containing 
plates  of  aluminum  and  lead.  The  lead  plates  were  10  by  2J 
inches  in  area,  and  yg-  inch  in  thickness.  The  aluminum  plates 
were  1  inch  by  10  inches,  also  of  yg-  inch  thickness. 

It  was  found  that  the  dimensions  of  the  electrodes,  jars,  etc., 
were  of  no  special  consequence,  and  that  equally  good  results 
were  obtained  when  lead,  iron  or  carbon  were  used  for'  the 
inactive  pole. 


AN  ELECTROLYTIC  CURRENT  RECTIFIER 


55 


EXPERIMENT  NO.  17 
TESTING  A   NODON  VALVE   WITH  DRY   CELLS 

When  the  aluminum  pole  of  one  of  these  valves  was  con- 
nected with  the  carbon  pole  of  a  battery  of  two  dry  cells,  and  a 
voltmeter  was  included  in  the  circuit,  the  latter  indicated  1-f- 
volts.  See  Fig.  19  (e.m.f.  of  cells  was  app.  2.8  volts).  The 
pointer  rapidly  dropped  to  nearly  zero,  finally  becoming  station- 
ary at  0.11  volt.  When  the  test  was  repeated  with  a  milli- 
ammeter,  the  initial  current  was  0.40  ampere,  which  finally 
dropped  to  0.0015  ampere,  where  it  remained. 


J 


D.C. VOLTMETER  DRY  CELLS 

FIG.  19. — TESTING  A  NODON  VALVE  WITH  DRY  CELLS. 

The  initial  current  is  of  course  affected  by  resistance  of  instru- 
ment and  leads,  the  dimensions  of  the  valve,  etc. 

The  Action  of  a  Nodon  Valve 

The  reason  why  a  Nodon  valve  permits  a  flow  of  current 
practically  in  only  one  direction  is  substantially  as  follows: 

When  a  direct  current  is  passed  through  a  solution  made 
of  bicarbonate  of  soda,  ammonium  phosphate  or  any  similar 
alkali,  by  means  of  two  pieces  of  immersed  iron,  lead  or  carbon, 
it  will  be  found  that  gas  bubbles  form  on  the  plates,  and  will 
rise  freely  to  the  surface.  If  alternating  current  be  used  instead, 
almost  no  gas  is  formed.  In  either  case  the  liquid  acts  as  a  resistor, 
which  can  be  shown  by  connecting  an  ammeter  in  series  and 
changing  the  distance  between  the  plates.  The  temperature 
of  the  solution  is  raised  by  the  passage  of  the  current. 

When,  as  stated  in  Experiment  No.  17,  a  strip  of  aluminum 
takes  the  place  of  one  of  these  lead  or  carbon  plates,  it  will  be 


56  EXPERIMENTAL  ELECTRICAL  TESTING 

found  that  the  current  will  still  flow  freely  when  the  circuit  is 
completed  with  the  (+)  plus  pole  of  the  battery  connected  with 
the  lead  or  carbon. 

But,  if  the  +  pole  is  connected  with  the  aluminum,  the 
initial  current  rapidly  diminishes.  This  is  partly  due  to  the 
fact  that  gas  bubbles  form  on  *he  aluminum  plate,  and  rise  to 
the  surface  of  the  liquid  as  they  are  crowded  off  by  others. 
These  gases  are  oxygen  and  hydrogen.  In  this  respect,  the  action 
of  the  valve  resembles  that  of  an  ordinary  simple  cell  consisting 
for  instance,  of  plates  of  zinc  and  copper,  dipped  in  an  acid 
solution.  But  there  is  another  and  more  complex  action  taking 
place.  Substantially,  the  aluminum  is  attacked  by  these  gases, 
which  combine  with  it  to  some  extent,  and  form  upon  its  surface 
a  non-conducting  layer  of  hydroxide  of  aluminum.  If  the  alum- 
inum plate  could  be  completely  covered  with  this  hydroxide,  it 
would  practically  become  a  non-conductor,  and  almost  all  elec- 
trical transmission  would  cease. 

The  fact  is,  however,  that  when  a  direct  current  is  used  as 
stated,  some  current  continues  to  flow  from  the  aluminum  to 
the  lead,  "  seeping  "  through  the  hydroxide  layer  (so  to  speak). 

When  alternating  current  is  used  instead  (with  a  single  valve) 
the  latter  may  be  said  to  open  and  close  successively  for  each 
cycle  so  that  one-half  of  each  alternating  current  wave  is  checked, 
the  other  half  passing  through  and  having  a  pulsating  direct 
effect.  The  valve,  however,  is  not  perfect  in  its  action,  and  may 
be  said  to  "  leak." 

EXPERIMENT  NO.  18 

TESTING  A  NODON  VALVE  WITH  A  DIRECT  CURRENT 
SERVICE  LINE 

When  one  of  these  valves  was  connected  with  a  source  of 
direct  current  (110  volts)  in  series  with  a  lamp  bank  and  an 
ammeter,  the  following  results  were  obtained  at  the  instant  the 
circuit  was  closed.  Plus  (+)  to  lead  pole,  1.95  amperes.  Plus 
(+)  to  aluminum  pole,  1.10  amperes. 

When  the  circuit  had  remained  closed  for  thirty  seconds  with 
+  to  aluminum,  the  current  was  reduced  to  0.15  ampere,  and  at 
the  end  of  two  minutes  the  total  current  flowing  as  indicated 
by  a  direct  current  milliammeter  was  0.020  ampere. 


AN  ELECTROLYTIC  CURRENT  RECTIFIER 


57 


EXPERIMENT   NO.    19 

TESTING   A   NODON   VALVE   WITH  ALTERNATING 
CURRENT 

When  alternating  current  is  used  in  connection  with  a  Nodon 
Valve,  it  is  assumed  as  already  explained,  that  pulsating  direct 
current  is  obtained,  since  current  is  not  supposed  to  flow  from 
the  aluminum  to  the  lead. 

While  this  is  not  strictly  the  case,  there  is  enough  interference 
to  produce  a  current  which  is  sufficiently  direct  to  be  measurable 
by  means  of  a  direct  current  movable  coil  permanent  magnet 
ammeter  or  voltmeter. 

But  such  an  instrument  will  respond  only  to  the  direct  cur- 
rent pulsations,  and  since  a  Nodon  Valve  will  by  no  means  rectify 


A.C.AM  METER 


TOA.C.LINE 


FIG.  20. — TESTING  A  NODON  VALVE  WITH  ALTERNATING  CURRENT. 
Instruments    required    are  a  Model    280    Weston    Ammeter,   range  5 
amperes,  and  a  Weston  Model  155  A.C.  Ammeter,  range  5  amperes. 

the  current  entirely,  the  results  obtained  when  the  so-called 
direct  current  is  tested  with  accurate  instruments  will  seem 
perplexing  and  apparently  paradoxical. 

For  instance,  when  both  an  alternating  and  a  direct  current 
ammeter  were  connected  in  series  with  a  Nodon  Valve,  a  lamp 
bank  and  a  source  of  110-volt  alternating  current  (see  Fig.  20), 
the  following  results  were  obtained : 


Time  in  Minutes. 

A  C  Line 

110  Volts. 

0 

1 

2 

3 

4 

5 

10 

D.  C.  Instr  

0.05 

0.50 

0.61 

0.65 

0.67 

0.67 

0.69  ampere 

A.  C.  Instr  

1.80 

1.30 

1.25 

1.23 

1.23 

1.24 

1  .  25  amperes 

58 


EXPERIMENTAL  ELECTRICAL  TESTING 


EXPERIMENT   NO.   20 
EFFICIENCY  TEST   OF  A   NODON  VALVE 

In  order  to  further  investigate  this  matter,  instruments 
were  added  to  the  circuit  until  the  general  arrangement  was  as 
shown  on  Fig.  21.  The  apparatus  consisted  of  a  Weston  Standard 
Wattmeter  connected  with  the  A.C.  line,  directly  indicating  the 
power  consumed.  The  instruments  used  for  measuring  the 
direct  current  were  one  Model  280  Voltmeter  and  one  Model 


D.C. AMMETER  A.C.AMMETER 

FIG.  21. — EFFICIENCY  TEST  OF  A  NODON  VALVE. 


280  Ammeter,  which  indicate  with  direct  current  only;  one 
Model  155  Voltmeter  and  one  Model  155  Ammeter.  The  Model 
155  instruments  are  of  the  "  soft-iron  "  type  and  are  operative 
with  either  direct  or  alternating  current.  Following  are  the 
results  obtained : 

WATTS  ON  A.   C.   LINE   150.0 


Line  Voltage,  110  A.  C. 

Volts. 

Amp. 

Watts. 

Direct  current  instruments  

36  5 

0  9 

32.8  + 

Alternating  current  instruments 

64  0 

1  65 

105  6 

AN  ELECTROLYTIC  CURRENT  RECTIFIER 


59 


EXPERIMENT  NO.  21 
EFFICIENCY   TEST  WITH   TWO  NODON  VALVES  IN  SERIES 

Two  valves  were  then  employed  in  series  (lead  to  aluminum) 
but  there  was  no  important  difference  in  efficiency,  as  shown  by 
the  following  data: 

WATTS   ON  A.C.   LINE   138 


Volts. 

Amp. 

Watts. 

Direct  current  instruments             .    .  . 

27  5 

0.94 

28.85 

Alternating  current  instruments  

46.5 

1.55 

72.07 

EXPERIMENT  NO.  22 
PUNCTURING  THE  INSULATING  WALL  OF  A  NODON  VALVE 

We  have  already  found  by  Experiment  No.  20  that  a  direct 
current  and  an  alternating  current  ammeter  connected  in  series 
with  each  other  and  operated  through  a  Nodon  valve  will  not 
give  corresponding  indications.  The  reason  for  this  is  fully 
explained  in  due  course. 

But  meanwhile,  an  interesting  little  experiment  (original, 
we  believe)  may  be  easily  performed,  which  consists  in  "  punch- 
ing a  hole  in  the  insulating  wall."  All  that  is  required  for  this 
operation  is  an  alternating  current  outfit  as  shown  on  Fig.  20 
and  a  piece  of  stiff  iron  wire,  one  end  of  which  is  bent  at  right 
angles  to  form  a  hook  about  2  inches  long.  The  end  of  this  hook 
should  have  a  sharp  point. 

If  the  aluminum  plate  is  touched  below  the  surface  of  the 
liquid  with  this  iron  point,  the  direct-current  ammeter  instantly 
drops  to  nearly  zero,  and  the  total  current  increases,  as  indicated 
by  the  alternating  current  ammeter  and  the  improved  luminosit}^ 
of  the  lamp.  See  Fig.  22. 

If  about  eight  lamps  (16  c.p.)  are  connected  in  multiple 
for  a  load  instead  of  only  one,  so  that  the  current  will  be  about 


60 


EXPERIMENTAL  ELECTRICAL  TESTING 


three  amperes,  the  point  of  the  hook  will  adhere  to  the  aluminum 
to  some  extent,  as  if  it  were  fused  in  by  the  action  of  the  current. 
,  Bubbles  rise  freely  from  the  hook  while  in  contact  with  the 
aluminum,  indicating  that  the  aluminum  hydroxide  will  not 
adhere  to  the  iron;  and  hence,  since  the  point  of  the  hook  has  been 
forced  through  the  layer,  it  conducts  current  from  the  aluminum 
through  the  liquid  to  the  lead,  changing  the  apparatus  into  a 
simple  liquid  resistor. 

Only  one  valve  should  be  used  to  get  the  best  effect  in  this  test. 


Construction  and  Arrangement  of  the  Electrolytic  Currrent 

Rectifier 

It  is  obvious  that  the  only  effect  produced  by  one  or  more 
Nodon  valves  in  series,  is  to  impede  the  flow  of  an  alternating 

current  in  one  direction.  The 
resultant  direct  current  cannot 
have  an  efficiency  greater  than 
50  per  cent  of  the  total  alter- 
nating current,  and  is  actually 
only  about  25  per  cent  or  less. 
It  is  possible,  however,  to  obtain 
greater  efficiency  by  arranging 
four  valves  in  the  form  of  a 
parallelogram  and  connecting  the 
alternating  current  in  such  a 
manner  that  both  halves  of  the 
current  will  be  utilized  to  pro- 
duce a  direct  current. 

One  of  these  rectifiers  was 
purchased  for  experimental  pur- 
poses and  tested  in  the  Weston 

laboratories.  It  consisted  of  four  porcelain  jars,  each  about 
5J  inches  in  diameter  and  11  inches  in  height,  provided  with 
an  insulated  top  and  binding  posts. 

Each  jar  contained  a  rod  of  aluminum  and  two  plates  of  lead, 
the  latter  being  connected  together.  The  solution  used  was 
bicarbonate  of  soda.  The  general  design  was  such  that  a  large 
percentage  of  the  alternating  current  was  converted  into  direct 
current. 


FIG.  22. — PUNCTURING   THE  INSU- 
LATING WALL  OF  A  NODON  VALVE. 


AN  ELECTROLYTIC  CURRENT  RECTIFIER 


61 


The  Theoretical  Operation  of  the  Electrolytic  Current 
Rectifiers 

The  current  from  an  A.C.  source  enters  at  a,  See  Fig.  23> 
is  checked  at  k,  but  may  flow  through  the  lead  plate  b  to  c  to  d, 
is  again  checked  at  i,  but  may  flow  through  the  instrument  (or 
load)  to  e,  continue  through  /  and  g  and  out  to  h,  constituting 
half  a  cycle.  The  other  half  operates  through  h,  is  checked  at 


A.C. LINE 


D.C.  VOLTMETER 


A.C. LINE 


ic'j.  23. — THE  ELECTROLYTIC  CURRENT  RECTIFIER. 


g,  but  follows  j  and  i  to  d,  is  checked  at  c  and  flows  through 
the  instrument  to  e,  etc. 

A  rather  surprising  feature  of  these  rectifiers  is  that  the 
direct-current  voltage  of  the  apparatus  when  the  voltmeter 
is  connected  as  shown  on  Fig.  23  is  sometimes  20  per  cent  higher 
than  the  A.C.  line  voltage.  This  is  only  the  case,  however, 
when  the  direct  current  used  is  negligibly  small. 


62 


EXPEEIMENTAL  ELECTRICAL  TESTING 


EXPERIMENT  NO.  23 

EFFICIENCY    TESTS    OF    A    COMMERCIAL    ELECTROLYTIC 
CURRENT   RECTIFIER 

In  order  to  obtain  some  data  in  relation  to  efficiency,  a  test 
was  made  having  a  continuous  Tun  of  two  hours.  See  Fig.  24. 
Following  are  the  results  obtained: 

A.C.   LINE,   VOLTAGE   110 


Pulsating  Direct  Current. 

Watts  on 
A.C.  Line. 

Tern,  of 
Solution. 

Efficiency. 

Volts. 

Amp. 

Watts. 

Time. 

320 

85.0 

1.70 

144.5 

0 

23°  C. 

45.1% 

380 

87.0 

1.72 

149.6 

1  hr. 

32°  C. 

39.4% 

450 

85.0 

1.70 

144.5 

2  hrs. 

42°  C. 

32.1% 

FIG.  24. — EFFICIENCY   TEST   OF   AN   ELECTROLYTIC    CURRENT   RECTIFIER. 


When  the  apparatus  was  connected  directly  with  the  A.C. 
line  and  no  direct  current  was  drawn,  45  watts  were  consumed. 
When  nothing  but  a  high  resistance  voltmeter  was  connected 
with  the  direct-current  binding  posts,  it  indicated  133  volts. 

Alternating-current  voltmeters  and  ammeters  were  also 
used  in  making  this  test.  Their  indications  taken  simulta- 


AN  ELECTROLYTIC  CURRENT  RECTIFIER 


63 


neously  with  the  direct  current  observations  averaged  1 1  per  cent 
higher. 

Some  experimenters  state  they  have  obtained  greater  effi- 
ciency by  introducing  a  transformer  in  the  circuit  so  as  to  reduce 
the  voltage  to  55  or  below. 

Following  is  the  result  of  a  test  made  under  such  conditions: 

A.C.   VOLTAGE  55 


Pulsating  Direct  Current. 

Watts  on 
A.C.  Line. 

Tern,  of 
Solution. 

Efficiency. 

Volts. 

Amp. 

Watts. 

Hours. 

88.0 

25.1 

1.27 

31.88 

0 

25.  2  C. 

36.2% 

80.0 

22.0 

1.10 

24.20 

1 

28.  OC. 

30.2% 

76.0 

20.1 

1.05 

21.10 

2 

30.  OC. 

27.7% 

NOTE. — It  should  be  distinctly  understood  that  it  is  not 
claimed  that  either  of  the  results  obtained  is  conclusive.  On 
the  contrary,  it  is  quite  probable  that  increased  efficiency  maybe 
obtained.  It  is  also  likely  that  some  modifications  of  the 
apparatus  including  a  water  jacket  or  some  other  contrivance 
for  keeping  the  temperature  from  rising  unduly  would  have 
advantages. 

Caution.  It  is  safest  to  include  a  lamp  bank  or  some  other 
resistor  in  the  line  when  the  rectifier  is  first  used  or  after  it  has 
been  idle  for  even  a  short  time.  There  is  often  a  current  surge 
of  20  or  more  amperes  when  the  circuit  is  first  closed.  This  is 
due  to  the  fact  that  the  hydroxide  has  not  had  time  to  form.  This 
surge  also  causes  a  strong  pulsating  current  to  develop  at  times, 
and  unless  fuses  are  put  in  both  lines,  damage  may  be  done  to 
apparatus  in  circuit. 

These  rectifiers  may  be  used  to  charge  small  storage  batter- 
ies, but  care  should  be  taken  to  connect  an  ammeter  in  circuit 
together  with  a  rheostat  or  bank  of  lamps,  in  order  to  regulate 
the  current. 

The  top  part  of  the  jars  as  well  as  the  cover  to  which  the 
elements  are  fastened  should  be  dipped  in  hot  paraffin  before 
setting  up,  so  as  to  prevent  the  solution  from  creeping. 

The  liquid  should  occasionally  be  renewed,  since  it  seems 
to  deteriorate. 


64  EXPERIMENTAL  ELECTRICAL  TESTING 


Instrument  Indications  in  Connection  with  a  Rectifier 

The  reason  for  the  difference  between  the  indications  of  the 
direct  and  alternating  current  Weston  instruments  when  used 
to  measure  the  output  of  an  electrolytic  rectifier,  is  explained 
in  an  article  by  Albert  Nodon,  in  Vol.  I,  of  the  Transactions  of 
the  International  Electrical  Congpess,  St.  Louis,  1904,  entitled 
"  Electrolytic  Rectifiers— An  Experimental  Research,"  page  510. 

This  experimental  research  includes  charts  showing  the 
wave  form  of  the  rectified  current  as  obtained  by  means  of  the 
ondograph  or  oscillograph. 

If  this  rectified  current  is  measured  by  a  Weston  alternating 
current  ammeter,  the  result  is  that  the  instrument  readings 
represent  the  effective  current,  which  will  be  the  square  root  of 
the  mean  square  of  the  instantaneous  values. 

Whereas,  if  a  direct-current  ammeter  is  used,  its  indications 
depend  upon  the  arithmetic  mean  value  of  the  instantaneous 
values  of  the  pulsating  current.  If  the  transformation  were 
perfect  the  difference  between  the  indication  of  the  two  types 
of  instruments  would.be  11  per  cent. 

The  fact  is,  however,  that  the  transformation  is  not  perfect. 
The  results  obtained  with  a  single  valve  prove  this,  and  even 
when  four  valves  are  arranged  in  parallelogram  form,  there  is 
a  loss  due  to  leakage  as  well  as  to  resistance.  This  can  be 
directly  proven  by  measuring  the  pulsating  current  by  means 
of  an  induction  meter  which  will  not  indicate  with  direct  current. 
It  can  be  simultaneously  shown  that  the  direct-current  instru- 
ment responds  only  to  the  direct-current  pulsations;  the  alternat- 
ing current  instrument  gives  the  combined  affect  of  direct  and 
alternating  current;  and  the  induction  meter  indicates  only  the 
alternating  current  (or  leakage),  its  indications  being  approxi- 
mately the  difference  between  the  other  indications. 

In  charging  storage  cells  and  in  running  direct-current  motors 
as  well  as  in  the  electro-disposition  of  metals,  the  above  state- 
ments should  be  taken  into  consideration,  since  it  is  obvious 
that  the  only  effective  current  for  such  work  obtained  from 
rectifiers  of  this  type  will  be  due  to  the  direct-current  pulsations. 

An  article  entitled  "  The  Chemistry  of  the  Electrolytic 
Current  Rectifier,"  by  Donald  McNicol,  will  be  found  in  the 
August,  1913,  number  of  the  "  Electrician  and  Mechanic." 


WESTON  DIRECT  CURRENT  MOVABLE  COIL  SYSTEM    65 


THE  WESTON  DIRECT  CURRENT  MOVABLE  COIL  SYSTEM 

(Prepared  by  the  Compiler) 

This  system  consists  primarily  of  a  coil  which  can  rotate 
freely  in  a  strong  magnetic  field  produced  by  means  of  a  per- 
manent magnet.  When  a  current  is  flowing  through  it,  this 
coil  acquires  magnetic  properties  and  tends  to  assume  a  position 
which  will  reduce  the  distance  between  its  poles  and  the  oppo- 
sitely magnetized  poles  of  the  permanent  magnet.  Springs 
which  also  serve  as  current  conductors  tend  to  oppose  the  move- 
ment of  the  coil.* 

The  Milliammeter 

An  instrument  which  consists  only  of  a  coil,  a  magnet,  a  core 
and  an  elastic  metallic  conductor  for  controlling  the  movement 
of  the  coil,  in  short  a  "  system  "  as  described  above,  is  in  its 
simplest  form  a  milliammeter.  All  Weston  direct-current  mov- 
able-coil systems  are  fundamentally  uncalibrated  milliammeters, 
although  they  may  differ  in  size,  in  the  strength  of  their  magnetic 
fields,  in  the  number  of  turns  of  wire  in  their  movable  coils,  and 
in  mechanical  details.  This  is  the  case  because  all  systems  of 
this  type  are  operated  by  means  of  a  small  current;  and  the 
extent  of  the  deflection  produced  depends  upon  the  strength 
of  this  current. 

The  Millivoltmeter 

The  system  as  described,  is  also  an  uncalibrated  potential 
indicator  of  millivoltmeter,  because  a  definite  electromotive 
force  is  needed  to  overcome  the  resistance  of  the  movable  coil 
and  force  a  current  through  it.  If,  therefore,  we  consider  the 
system  in  its  simplest  form  as  consisting  only  of  a  movable  coil, 
a  core,  a  magnet,  and  a  pair  of  springs  directly  connected  to  a 

*  See  also  Monograph  B-2. 


66  EXPERIMENTAL  ELECTRICAL  TESTING 

pair  of  binding  posts  by  means  of  leads  of  negligible  resistance, 
then  it  follows  that,  for  any  deflection  of  the  moiable  coil  at  a  fixed 
temperature  the  current  will  always  be  the  same  for  that  deflection. 
And  since  the  resistance  of  the  movable  coil  and  springs  will 
always  be  the  same  at  a  fixed  temperature,  it  also  follows  that 
under  the  given  conditions  the  electro-motive  force  required  to 
overcome  the  resistance  of  the  movable  coil,  etc.,  and  produce 
any  desired  current,  will  always  be  the  same  unless  extra  resist- 
ance is  added  to  the  circuit. 

The  Movable  Coil  Constant 

The  movable  coil  constant  is  the  component  of  current  and 
e.m.f.  pertaining  to  a  particular  system,  that  is  to  say,  a  system 
of  a  certain  type  or  class;  and  under  all  normal  conditions  such 
constants  are  fixed  and  unchangeable.  For  instance,  if  the 
current  required  to  obtain  a  full  scale  deflection  is  .01  ampere, 
and  (r)  the  resistance  of  the  movement  is  6  ohms,  then  the  e.m.f., 
required  will  be  E  =  Ir,  in  this  instance  being 

6 X. 01  =  .06  volt, 
and  the  power  required  to  produce  a  full-scale  deflection  will  be 

.01 X  .06  =  .0006  watt. 

To  extend  the  range  of  such  an  instrument  for  voltage  meas- 
urements, it  will  be  necessary  to  add  a  resistor  to  the  circuit, 
and  the  resistance  of  such  a  resistor  in  ohms  per  volt  is  found 

E 
by  the  formula  R=——r. 

For  instance,  to  obtain  a  1-volt  range,  the  added  resistance 
in  this  instance  will  be: 

#  =  -rrr-6=9 

Necessarily,  to  make  a  100-volt  instrument  of  the  movement, 
a  total  resistance  of  10,000  ohms  will  be  required,  and  all  other 
ranges  will  have  a  directly  proportionate  resistance. 


WESTON  DIRECT  CURRENT  MOVABLE  COIL  SYSTEM    67 


The  Ammeter* 

In  attempting  to  use  the  movement  already  referred  to  for 
current  measurements,  it  will  be  apparent  immediately  that 
no  current  greater  than  .010  ampere  should  be  passed  through  it. 
If  therefore  a  larger  current  than  this  is  to  measured,  some 
contrivance  must  be  attached  which  will  permit  a  larger  cur- 
rent to  flow,  and  yet  limit  the  quantity  flowing  through  the  move- 
ment. This  is  most  easily  accomplished  by  means  of  a  divided 
or  shunted  circuit. 

For  instance,  if  a  resistor  is  constructed  of  insulated  wire 
having  the  same  resistance  as  the  movement,  and  is  connected 
directly  with  the  binding  posts  of  the  instrument,  and  the 
binding  posts  are  then  connected  with  a  source  of  current,  it  may 
be  deduced  that  such  a  current  will  split;  and  since  the  resistor 
has  the  same  resistance  as  the  movable  coil,  the  current  will 
split  evenly,  half  of  it  going  through  the  movement  and  half 
through  the  resistor.  But,  the  movement  will  only  respond  to 
the  current  flowing  through  it,  and  not  to  the  current  flowing 
through  the  resistor.  Since  these  currents  are  alike,  it  follows 
that  the  pointer  will  indicate  half  of  the  total  current  flowing. 
In  other  words,  the  ampere  range  of  the  instrument  has  been 
doubled. 

To  determine  how  to  still  further  extend  the  ampere  range 
of  the  instrument  it  is  only  necessary  to  refer  to  the  laws  relat- 
ing to  divided  circuits.  The  current  flowing  through  two  parts 
of  a  divided  circuit  will  be  directly  proportional  to  the  resist- 
ances of  these  circuits.  If,  for  instance,  the  shunt  coil  measured 
.06  ohm  and  the  movement  6  ohms,  then  the  current  would 
be  as  .06  is  to  6,  that  is,  the  current  through  the  shunt  would  be 
100  times  as  great  as  that  passing  through  the  movement.  For 
it  must  not  be  forgotten  that  the  voltage,  at  the  binding  posts 
is  the  same  for  the  movement  as  it  is  for  the  shunt  coil,  and  that 


*  For  data  relating  to  Weston  movable  systems,  see  also  "  Elements  of 
Electricity,"  Timbie,  Chap.  XIV.;  "Physics,"  Mann  and  Twiss,  page  169; 
"  Practical  Physics/''  Black  and  Davis,  page  284;  "  Laboratory  Manual," 
Black  and  Davis,  page  64;  "  High  School  Physics,"  Carhart  and  Chute, 
page  371;  "A  High  School  Course  in  Physics,"  Gorton,  page  405;  "Elec- 
trical Instruments  and  Testing,"  Schneider  and  Hargrave,  Chap.  4,  and 
"  Lessons  in  Practical  Electricity,"  Swoope,  Lesson  18. 


68  EXPERIMENTAL  ELECTRICAL  TESTING 

consequently  the  less  the  resistance  of  the  shunt  the  greater  will 
be  the  current  flowing  through  it.  A  point  could  therefore  be 
reached  where  the  shunt  would  have  so  low  a  resistance  that  it 
would  carry  practically  all  of  the  current,  and  not  enough  would 
flow  through  the  movement  to  make  it  operative.  Such  a  shunt 
would  be  described  in  practice  ^s  not  having  enough  "  drop," 
meaning  that  the  potential  difference  between  its  extremes  would 
be  insufficient  for  the  purpose  for  which  it  was  intended. 

In  practical  work  the  shunts  are  usually  constructed  to  have 
a  standard  drop  of  50  or  100  millivolts.  The  resistance  of  the 
system  is  increased  by  adding  non-inductive  zero  temperature 
coefficient  material  in  series,  so  as  to  increase  the  e.m.f.  required 
to  produce  a  full  scale  deflection  to  50  or  100  millivolts  or  some 
other  value,  according  to  the  type  of  instrument,  and  the  drop 
of  the  shunt. 

THE   WESTON   ALTERNATING   AND   DIRECT- CURRENT 
"SOFT    IRON"    SYSTEM 

(Prepared  by  the  Compiler.) 

The  direct-current  movable-coil  system  described  in  the  pre- 
ceding article  is  inoperative  with  alternating  current,  because 
its  field  as  produced  by  a  permanent  magnet  has  fixed  polarity. 
Consequently  when  an  alternating  current  is  passed  through 
the  movement,  the  polarity  of  the  movable  coil  is  thereby  con- 
tinually reversed,  and  the  movement  oscillates  instead  of  being 
deflected.  The  effect  of  an  alternating  current  when  applied 
to  a  direct-current  movement  can  be  plainly  seen  by  the  vibra- 
tion of  the  pointer,*  but  of  course  there  is  no  continuous  motion 
in  one  direction  by  means  of  which  an  alternating  current  could 
be  measured. 

The  movable  element  of  the  Weston  soft-iron  system  con- 
sists of  a  small  curved  piece  of  iron  fastened  to  a  light  pivoted 
shaft.  This  shaft  is  also  provided  with  a  truss  form  of  pointer 
made  of  thin  aluminum  tubing,  to  which  is  attached  a  balance 
cross  and  a  small  vane.  The  shaft  moves  in  jeweled  bearings. 

*  Experiments  of  this  kind  if  protracted,  neither  improve  the  sharpness 
of  the  pivots  nor  lengthen  the  life  of  the  pointer  of  a  d.c.  instrument. 


FIG.  25. — PHANTOM  VIEW  OF  WESTON   MODELS  151,   155,   156,  159,  160. 
Moving  Parts  of  "Soft  Iron  "  Voltmeters. 


FIG.  26. — PHANTOM   VIEW  OF  WESTON  MODELS  151,   155,   156,   159,  160 
Moving  Parts  of  "  Soft  Iron  "  Ammeters. 


THE  WESTON  "SOFT-IRON"  SYSTEM  69 

Near  this  movable  element  and  concentric  with  it  is  a  small 
curved  tongue  of  soft  iron  which  is  rigidly  held  by  a  suitable 
support.  (See  Figs.  25  and  26.) 

Surrounding  these  is  a  field  coil,  made  up  either  of  a  large 
number  of  turns  of  insulated  wire  when  the  instrument  is  to  be 
used  for  the  measurement  e.m.f.  or  else  of  one  or  more  turns 
of  heavy  conducting  material,  when  designed  for  the  measurement 
of  current. 

Principle  of  Operation.  When  a  direct  current  is  passed 
through  the  field,  the  movable  element  and  the  fixed  tongue 
of  iron  become  magnetized  by  induction;  but  since  they  are 
within  the  field  coil,  their  juxtaposed  ends  will  have  like  polar- 
ities. Consequently  these  poles  will  repel  each  other.  The 
only  resultant  motion  possible  is  the  rotation  of  the  movable 
element. 

When  alternating  current  is  used,  the  polarity  of  the  field 
coil  will  be  alternately  North  and  South,  the  number  of  reversals 
depending  upon  the  frequency. 

The  polarities  of  the  movable  and  fixed  iron  parts  of  the 
system  will  also  reverse  correspondingly,  but  although  the  jux- 
taposed parts  will  have  constantly  reversing  polarities,  they  will 
have  like  polarities  in  relation  to  each  other,  and  therefore  will 
necessarily  repel  each  other  continuously,  thereby  imparting  a 
rapid  series  of  impulses  to  the  movable  element,  causing  a  deflec- 
tion in  one  direction  only. 

This  deflection  is  opposed  and  therefore  controlled  by  the 
action  of  a  delicate  spiral  spring;  hence  the  extent  of  the  rota- 
tion depends  upon  the  strength  of  the  current  flowing  through 
the  solenoid. 

The  peculiar  shapes  as  well  as  the  relative  positions  of  the 
iron  parts  are  patented  features  which  are  the  outcome  of  much 
theoretical  work  and  numerous  experiments.  As  a  result,  the 
instrument  is  almost  entirely  free  from  hysteresis  or  lag;  that  is 
to  say,  the  magnetization,  demagnetization,  and  remagneti- 
zation  of  the  iron,  will  be  practically  perfect. 

If  the  instrument  is  designed  for  current  measurements,  it 
is  so  arranged  that  all  of  the  current  passes  through  the  sole- 
noid or  field  coil.  This  is  also  the  case  when  intended  for  the 
measurement  of  e.m.f.,  but  an  adjusted  resistor  lies  in  series 
with  the  solenoid.  The  resistance  of  the  instrument  is  thereby 


70  EXPERIMENTAL  ELECTRICAL  TESTING 

increased,  and  the  quantity  of  current  which  may  flow  is  regu- 
lated. Precisely  as  in  direct  current  movable  coil  instruments, 
the  amount  of  current  which  will  flow,  depends  upon  the  e.m.f. 
of  the  circuit  across  which  the  instrument  is  connected. 

The  vane  or  damper  moves  in  a  fan-shaped  pocket  which  is 
shown  in  Fig.  26  with  the  cove^  removed.  When  this  vane  is 
enclosed  it  damps  the  movement  of  the  system  without  mechanical 
friction.  That  is  to  say,  the  vane  does  not  touch  any  part  of 
the  receptacle  but  moves  through  confined  air. 

The  scales  of  these  instruments  are  open  and  fairly  uniform 
throughout  four-fifths  of  the  total  range  of  deflection. 


CO-OPERATORS 

We  extend  our  hearty  thanks  to  all  physics  instructors  who 
have  assisted  in  the  preparation  of  this  monograph,  either  by 
their  encouraging  approval  of  our  previous  efforts,  or  by  their 
suggestions  and  direct  contributions. 

Among  many  others,  we  are  especially  indebted  to  the  science 
teachers  whose  names  we  append,  with  occasional  extracts  from 
their  communications: 

AMES,  C.  G.,  Instructor  in  Physics,  High  School,  Berkeley, 
Cal. 

"  I  would  be  glad  if  you  can  spare  me  two  extra  copies  of  monograph 
B-2  for  class  use." 

ANDREWS,  A.  P.,  Instructor,  Department  of  Physics,  Min- 
neapolis, Minn. 

"  There  can  be  no  possible  question  as  to  the  service  you  are  rendering 
schools.  Personally,  I  expect  to  profit  by  it." 

BAER,  C.  E.,  Department  of  Science,  The  Lincoln  High  School, 
Seattle,  Washington. 

"  Please  send  all  Monographs  or  other  literature  descriptive  of  such  of 
your  instruments  as  may  practically  be  used  in  our  modern  high  schools. 

I  am  on  a  committee  of  Seattle  Physics  teachers,  appointed  to  outline  a 
revised  course  in  electricity  from  beginning  to  end,  and  need  your  co-opera- 
tion." 


CO-OPERATORS  71 

BARBER,  FRED  D.,  Illinois  State  Normal  University,  Normal; 
111. 

BARRETT,  J.  T.,  Department  of  Physics,  Lawrenceville  School, 
Lawrenceville,  N.  J. 

"  Personally  I  was  glad  to  see  you  entering  a  field  where  Tin  Students' 
Instruments  had  been  the  only  low-priced  supplies  available." 

BEALS,  FREDERICK  H.,  Department  of  Physics,  Barringer 
High  School,  Newark,  N.  J.  Formerly  Prof,  of  Physics,  Occi- 
dental College,  Los  Angeles,  Cal. 

"  I  hope  you  will  continue  the  good  work  of  issuing  monographs  contain- 
ing experiments  of  practical  value,  experiments  from  the  commercial  testing 
laboratories  and  from  workshops,  exercises  more  nearly  touching  daily 
experience  and  commercial  life  than  have  hitherto  been  customary  in  school; 
real  problems  of  the  work-a-day,  experiments  which  have  living  reality  in 
the  school  laboratory." 

BLACK,  PROF.  N.  HENRY,  A.M.  Science  Master,  Roxbury 
Latin  School,  Boston,  Mass. 

"  I  have  yours  of  the  20th  inst.,  and  am  much  interested  in  your  efforts 
to  give  the  schools  a  really  good  electrical  measuring  instrument,  and  at  the 
same  time  to  suggest  how  they  may  be  used  to  get  nearer  to  the  real  practical 
electrical  problems.  You  may  be  interested  to  know  that  last  year  when 
I  was  getting  out  the  Laboratory  Manual  to  go  with  the  text-book,  your 
voltmeter  and  ammeter  was  the  only  form  of  electrical  direct-reading  instru- 
ment, which  I  felt  enough  confidence  in  to  illustrate.  (See  Fig.  38  of  Lab. 
Man.).  Go  ahead  with  this  good  work." 

BOYNTON,  W.  P.,  Professor  of  Physics,  University  of  Oregon, 
Eugene,  Oregon. 

"Your  monographs  are  of  interest  to  me  personally,  and  also  of  value, 
as  I  am  called  on  to  advise  present  and  prospective  teachers  in  physics  in 
the  High  Schools  of  this  State." 

BURGIN,  BRYAN  0.,  Department  of  Science,  Albany  High 
School,  Albany,  N.  Y. 

BURNS,  ELMER  E.,  Instructor  in  Physics,  Joseph  Medill 
High  School,  Chicago,  111. 

"  I  have  read  the  monograph  carefully  and  do  not  see  any  way  how  it 
could  be  improved." 

CADY,  W.  G.,  Professor  in  Physics,  Wesley  an  University, 
Middletown,  Conn. 

"  The  idea  of  issuing  these  monographs  is  a  good  one." 


72  EXPERIMENTAL  ELECTRICAL  TESTING 

CLARK,  M.  G.,  Superintendent  of  Public  Schools,  Sioux 
City,  Iowa. 

"  I  am  just  in  receipt  of  '  Elementary  Electrical  Testing/  and  wish  to 
take  this  opportunity  to  congratulate  you  upon  the  work  which  you  have 
done  in  bringing  practical  problems  of  industrial  life  directly  to  the  school. 
If  industrial  plants  in  general  would  take  this  same  attitude,  it  would  present, 
to  the  schools  a  challenge  which  they  couid  not  ignore. 

"  To  what  extent  and  in  what  way  could  I  secure  more  copies  of  this 
monograph?  " 

COLTON,  GEO.,  Professor  of  Physics,  Hiram  College,  Hiram, 
Ohio. 

"  I  appreciate  the  monographs  which  your  company  is  sending  out  and 
can  make  use  of  some  things  in  them  in  the  laboratory  work  of  my  students." 

DOWD,  MR.  J.  E.,  Classical  High  School,  Worcester,  Mass. 

"  I  will  state  that  your  monograph  proved  of  great  service  and  value 
to  me,  as  much  of  the  electrical  apparatus  we  have  is  of  your  make,  and 
the  topics  dwelt  upon  offered  much  information  about  them." 

DRAPER,  JASON  T.,  Master  in  Science,  High  School,  Holyoke, 

Mass. 

"  I  plan  to  equip  my  laboratory  at  once  with  whatever  is  needed  to  carry 
out  all  that  is  outlined  in  your  Monographs  in  Elementary  Testing." 

EASTMAN,  EARL,  Science  Department,  High  School,  Atlantic 
City,  N.  J. 

"  I  find  your  monograph  B-2  very  helpful." 

ECKERT,  ALBERT  C.,  Eastern  High  School,  Bay  City,  Mich. 
"  Your  monographs  have  proven  a  help  to  me.     I  have  adopted  several 
of  the  experiments  you  describe  in  my  laboratory  course." 

EDWARDS,  RAY  L.,  Professor  Physics  Department,  Park 
College,  Parkville,  Mo. 

"  I  was  very  glad  to  receive  the  monographs  B-l,  B-2  and  B-3." 

EGGEN,  H.  O.,  Instructor  in  Physics,  Santa  Ana  High  School, 
Santa  Ana,  Cal. 

"  Your  monographs  will  be  helpful  to  me  both  in  selecting  instruments 
and  in  selecting  experiments." 

EVANS,  WM.  F.,  Girls'  High  School,  Brooklyn,  N.  Y. 
FEE,  LEWIS  H.,  Head  of  Science  Department,  Everett  High 
School,  Everett,  Wash. 


CO-OPERATORS  73 

FISCHER,  H.  F.,  Professor  University  of  California,  Berkeley, 
Cal. 

FOERSTE,  AUGUST  F.,  Instructor  in  Physics,  Steele  High  School, 
Dayton,  Ohio. 

FLANDERS,   M.   M.,   Bliss  Electrical  School,  Takoma  Park, 
Washington,  D.  C. 

"  I  would  like  any  technical  data  you  will  furnish  in  regard  to  principle 
of  operation  of  your  soft-iron  instruments." 

Fox,  JOHN  E.,  Western  State  Normal  School,  Kalamazoo, 

Mich. 

"  I  think  your  plan  an  excellent  one  and  shall  be  glad  to  suggest  some 
materials  for  future  monographs  which  will  be  of  interest  to  physics  teachers." 

GARDINER,  F.,  Headmaster  of  the  Yeates  School,  Lancaster, 
Pa. 

"  I  should  like  to  see  experiments  in  efficiency  tests,  on  the  small  trans- 
former, electric  cooking  utensils  and  current  capacity  test  on  commercial 

fuses." 

GLENN,  EARL  R.,  Department  of  Physics,  Froebel  School, 
Gary,  Ind. 

"  I  have  read  the  literature  you  sent  with  great  interest  and  profit. 
Science  instructors  owe  much  to  the  company  you  represent." 

GORTON,  F.  R.,  Professor  of  Physics,  Michigan  State  Normal 
College,  Ypsilanti,  Mich. 

"  Your  communication  regarding  the  publication  of  B-4  compilation 
of  laboratory  exercises  is  at  hand.  I  think  the  subject  matter  excellent, 
but  feel  that  the  experimental  part  is  too  full  in  some  points  and  deficient 
in  others.  I  shall  be  glad  to  see  the  publication." 

GRAHAM,  PROF.  W.  P.,  College  of  Applied  Science,  Syracuse 
University,  Syracuse,  N.  Y. 

GRIFFIN,  CHAS.  E.,  Head  of  Science  Department,  San 
Bernardino  High  School,  San  Bernardino,  Cal. 

"  I  think  at  the  present  time  the  greatest  need  in  the  teaching  of  elec- 
tricity in  our  high  schools  is  an  apparatus  for  the  demonstration  of  alter- 
nating current  phenomena.  Your  plan  of  co-operation  appeals  to  me  as 
being  especially  desirable." 


74  EXPERIMENTAL  ELECTRICAL  TESTING 

HAMMOND,  H.  E.,  Physics  Department,  Kalamazoo  Public 
Schools,  Kalamazoo,  Mich. 

"  I  believe  your  company  is  doing  a  good  work  in  putting  out  these 
monographs,  and  I  think  that  there  ought  to  be  a  response  in  a  business  way, 
or  Weston  instruments  do  what  they  are  intended  to  do." 

HATHAWAY,  F.  R.,  Physics  Director,  Classical  High  School, 
Salem,  Mass. 

"  I  received  the  two  monographs  and  hope  to  take  advantage  of  the 
suggestions  contained  therein,  in  teaching  electricity  this  coming  winter." 

HEDRICK,  WM.  A.,  Instructor  in  Physics,  McKinley  Manual 
Training  School,  Washington,  D.  C. 

"  I  like  the  monographs  very  much  and  their  aid  has  persuaded  one  of 
the  teachers  to  try  the  drop  of  potential  along  a  wire,  that  I  was  not  able 
to  do  before.  We  will  take  great  pleasure  in  calling  the  attention  of  the 
physics  Teachers'  Ass'n  to  your  instructive  monographs." 

HULL,  PROF.  G.  F.,  Wilder  Laboratory,  Dartmouth  College, 
Hanover,  N.  H. 

"  You  are  doing  a  great  service  to  scientific  teachers  in  sending  out  this 
literature." 

INGVALSON,  EDWARD,  Instructor  in  Physics,  Lanesboro 
Public  Schools,  Lanesboro,  Minn. 

"  There  is  certainly  need  of  reform  as  far  as  Lab.  measuring  apparatus 
is  concerned,  and  I  believe  you  are  doing  much  good  in  circulating  such 
literature  as  your  monographs.  The  toy  apparatus  we  have  is  a  farce.  Most 
science  teachers  know  this  but  are  handicapped  in  improving  conditions." 

KELBER,  C.  M.,  Department  of  Physics  and  Chemistry, 
Petersburgh  High  School,  Petersburgh,  111. 

"  Perhaps  some  science  teachers  would  find  it  suggestive  if  you  were  to 
describe  a  method  for  making  efficiency  tests  of  commercial  electric  heating 
units  such  as  disk  stove,  percolator,  etc.  I  have  found  such  exercises  very 
conducive  to  interest  in  my  class  work." 

KILLEN,  A.  H.,  Instructor  in  Physics,  Flushing  High  School, 
Flushing,  N.  Y. 

LYON,  LESLIE  W.,  Department  of  Physical  Science,  Burling- 
ton High  School,  Burlington,  Iowa. 

"  I  would  particularly  like  to  have  discussed  the  measurement  of  electric 
power  in  such  experiments  as  determining  the  efficiency  of  electric  lights, 
electric  iron,  heating  plates,  etc." 


CO-OPERATORS  75 

MARBLE,  MILTON  M.,  Department  of  Physics,  New  Haven 
High  School,  New  Haven,  Conn. 

"  Please  send  with  instruments,  25  copies  of  Monograph  B-2  for  students' 
use,  and  oblige." 

MARVELL,  SUMNER  E.,  New  Bedford  High  School,  New 
Bedford,  Mass. 

"  I  found  your  monographs  helpful  in  the  physics  work  of  the  school. 
I  have  always  felt  that  a  closer  contact  between  our  teaching  and  commercial 
apparatus  would  be  of  great  assistance  to  us." 

MCKENZIE,  MONROE  R.,  Professor  of  Physics,  Parsons  Col- 
lege, Fairneld,  Iowa. 

MOORE,  PROF.  J.  C.,  Master  in  Science,  Worcester  Academy, 
Worcester,  Mass. 

"  I  wish  to  say  that  the  monographs,  especially  B-2  and  B-3,  are  excep- 
tionally useful  to  science  teachers.  We  hope  that  you  will  continue  to  issue 
them  and  suggest  practical  work  in  electrical  measurement.  You  will  doubt- 
less be  interested  to  know  that  they  have  stimulated  us  to  equip  a  labora- 
tory for  electrical  work,  separate  from  our  regular  physics  laboratory." 

MOORE,  J.  COLIN,  Instructor  in  Electricity,  Lake  High  Manual 
Training  School,  Chicago,  111. 

"  I  shall  be  glad  to  make  some  suggestions  for  experiments  which  may 
be  of  use  to  others." 

NYE,  ARTHUR  W.,  Department  of  Electrical  Engineering 
University  of  Southern  California,  Los  Angeles,  Cal. 

"  I  received  the  monographs  early  in  the  summer  and  was  favorably 
impressed  with  them.  I  hope  that  you  will  continue  their  publication  and 
that  you  will  also  publish  some  dealing  with  high-grade  electrical  instruments. 
There  seems  to  be  a  lack  of  printed  material  about  really  high  grade  practical 
engineering  electrical  measurements." 

PACE,  Miss  LILLIAN,  Central  High  School,  Washington,  D.  C. 

"  I  have  always  thought  that  something  of  the  sort  sent  out  by  makers 
of  instruments  which  we  use  would  be  most  acceptable  and  am  glad  you  have 
entered  in  this  work.  It  will  give  me  pleasure  to  co-operate  with  you  and  make 
suggestions." 

PEET,  J.  C.,  Department  of  Electricity  and  Chemistry, 
Technical  High  School,  Harrisburg,  Pa. 

"  Your  experiment  on  the  Heating  Effect  of  current  is  especially  good. 
I  should  like  to  see  you  add  one  on  Chemical  Effect,  using  the  copper  volt- 


76  EXPERIMENTAL  ELECTRICAL  TESTING 

meter   to    standardize   an    ammeter.     Keep    up   the  good  work  started  in 
these  monographs." 

PHILIPPI,  H.  C.,  Department  of  Physics,  State  Normal  School, 
Bellingham,  Wash. 

"  I  should  be  glad  to  have  you  discuss  in  future  monographs  any  practical 
electrical  measurements  suitable  for  high-school  work  or  for  the  first  two 
years  of  college  physics." 

POND,  ETHEL  C.,  Physics  Teacher,  Sycamore  High  School, 
Sycamore,  111. 

"  I  consider  publications  such  as  yours  the  most  valuable  help  a  physics 
teacher  can  receive,  and  I  wish  to  express  my  appreciation." 

POORE,  CHAS.  D.,  The  Northern  Normal  and  Industrial 
School,  Aberdeen,  South  Dakota. 

"  I  remember  on  getting  your  monographs,  of  at  once  being  struck  with 
the  need  of  just  such  things  in  perfecting  my  electrical  course." 

RANDALL,  J.  A.,  Pratt  Institute,  Brooklyn,  N.  Y. 

RATCLIFF,  R.  F.,  Department  of  Physics  and  Chemistry, 
Central  Normal  School,  Danville,  Ind. 

"  Monograph  B-2  is  very  valuable  to  us,  especially,  in  that  it  gives 
sample  experiments  from  the  practical  electrician's  point  of  view.  This  is 
a  phase  of  the  work  we  wish  to  develop." 

REED,  HAROLD  B.,  East  High  School,  Cleveland,  Ohio. 

"  Have  read  the  monographs  with  the  greatest  interest.  They  are  a 
real  contribution.  Shall  try  out  several  of  these  experiments  this  year. 
Shall  be  glad  to  do  anything  possible  to  help  along  a  good  cause." 

RIAL,  DAVID,  Instructor  in  Physics,  State  Normal  School, 
Mansfield,  Pa. 

ROOD,  JAMES  T.,  Professor  of  Physics  and  Engineering, 
Lafayette  College,  Easton,  Pa. 

"  Your  idea  that  these  monographs  shall  have  so  much  intrinsic  merit 
that  they  will  be  carefully  kept  in  file  as  matter  of  value,  is,  I  think,  most 
admirable.  Prosit! " 

ROTHERMEL,  JOHN  J.,  Physics  Laboratory,  Eastern  High 
School,  Washington,  D.  C. 

"  I  hope  to  be  able  to  take  some  work  on  efficiency  tests  of  small  trans- 
formers, and  probably  also  in  electric  cooking  utensils.  I  should  be  very 
glad  to  have  about  half  a  dozen  copies  of  Monograph  B-2  and  B-3  that  I 
could  use  with  one  of  my  classes  in  their  electrical  experiments  this  year." 


CO-OPERATORS:,  J  ;'  0^:''-:::  A    77 

SMITH,  ERNEST  REVELEY,  Instructor  in  Physics,  Syracuse 
High  School,  Syracuse,  N.  Y. 

TURNER,  GEO.  M.,  Hasten  Park  High  School,  Buffalo,  N.  Y. 

"  Our  work  with  the  triple-range  voltmeters  and  double-range  ammeters 
Model  280  proved  very  satisfactory.  No  instrument  was  abused  by  any 
pupil  either  by  accident  or  intent.  It  is  our  purpose  to  extend  their  use 
during  the  course  in  electrical  work  of  the  present  school  year. 

TWINING,  H.  L.,  Head  of  Physics  and  Electrical  Engineering, 
Los  Angeles  High  School,  Los  Angeles,  Cal. 

"  You  are  making  a  move  in  the  right  direction  in  developing  instruments 
of  accuracy  for  high  schools.  I  am  writing  a  text  on  elementary  electricity 
covering  the  first  year's  work  and  also  a  manual  to  accompany  it.  In  it  I 
am  going  to  feature  your  instruments  and  recommend  their  use.  I  do  this 
because  they  are  the  best  that  the  world  has  to  offer." 

Twiss,  G.  R.,  Professor  of  Physics,  Ohio  State  University, 
Columbus,  Ohio. 

"  Replying  to  your  letter  of  January  21st,  which  has  been  overlooked 
because  of  the  pressure  of  semester  examinations,  I  would  say  that  I  am 
very  much  interested  in  your  enterprise  looking  to  the  publication  of  mono- 
graphs on  experiments  that  can  be  made  with  standard  commercial  instru- 
ments, and  that  have  direct  commercial  and  industrial  bearings.  I  think 
that  if  wide  publicity  is  given  to  such  experiments,  the  movement  cannot 
fail  to  be  productive  of  much  good  to  the  pupils  of  the  high  schools.  I 
should  be  glad  to  receive  all  the  pamphlets  of  this  character  that  you  have 
issued  up  to  date,  and  to  be  placed  on  your  mailing  list  for  other  material  of 
similar  interest  that  you  may  issue  from  time  to  time." 

VAWTER,  C.  E.,  Professor  of  Physics,  Virginia  Polytechnic 
Institute,  Blacksburgh,  Va. 

"  I  have  four  of  your  minature  instruments  and  I  consider  them  the 
greatest  find  that  I  have  made  for  my  electrical  work  in  a  long  time.  I  shall 
get  more." 

WATJCHOPE,  PROF.  J.  A.,  Department  of  Physics,  Mechanics 
Arts  High  School,  St.  Paul,  Minn. 

"  I  sincerely  hope  you  will  continue  the  publication  of  the  monographs, 
as  the  suggestions  are  helpful  to  me  and  I  am  sure  must  be  to  many  other 
teachers.  This  is  excellent  work  that  you  are  doing." 

WEBSTER,  EVANS,  Head  of  Physics  Department,  English 
High  School,  City  of  Lynn,  Mass. 

"  What  we  need  most  in  our  elementary  laboratories  is  a  galvanometer 
in  portable  form  for  use  with  the  slide  wire  bridge,  and  which  can  be  used 


78  EXPERIMENTAL  ELECTRICAL  TESTING 

without  a  shunt  box,  costing  not  over  six  or  seven  dollars.  The  galvanom- 
eters usually  found  (made  by  .  .  .  )  are  the  most  exasperating  pieces  of 
apparatus  to  put  in  the  hands  of  students  that  I  know  of." 

WOOD,  LYNN  H.,  Professor  Department  of  Physical  Science, 
Union  College,  College  Point  View,  Neb. 

"  We  have  received  your  monographs  B-l,  B-2  and  B-3.  We  appreciate 
them  very  much.  For  a  long  time  the  w*ork  in  electricity  in  our  science 
department  has  been  altogether  too  theoretical,  and  we  welcome  any  changes 
that  will  tend  to  make  the  work  more  practical.  We  are  adopting  many  of 
the  experiments  which  you  give  in  these  monographs." 

WYLIE,  R.  M.,  Professor  of  Physics,  Marshall  College,  Hunt- 
ington,  W.  Va. 

"  Most  high  schools  buy  their  equipment  as  you  know,  to  fit  their  partic- 
ular course.  If  the  laboratory  manuals  which  are  put  out  by  the  book 
companies  to  accompany  such  texts  as  Milliken  &  Gale,  Carhart  &  Chute, 
Gorton,  or  Hoadley's  new  book,  only  contained  cuts  of  your  minature 
instruments  and  precise  directions  for  their  use  in  the  experiments  in  elec- 
tricity, you  would  find  many  schools  trying  yours  and  using  them." 


AN  APPEAL 


If  our  monographs  are  of  service  to  the  reader,  if 
we  have  succeeded  in  bringing  him  in  touch  with  the 
earnest  efforts  of  others,  then,  from  a  utilitarian  stand- 
point, it  would  seem  that  the  most  suitable  return 
any  physics  instructor  can  make,  will  be  to  recipro- 
cate with  new  material  or  helpful  suggestions,  through 
the  medium  of  our  publications. 


THIS  BOOK  IS  DUE  ON  THE  LAST  BATE 
STAMPED  BELOW 

AN     INITIAL    FINE      OF     25     CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  D*TE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 


1933 


USE 
OCT2    196 


°OT  8     196) 


LD  21- 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


